one of the latest and most important of these discoveries has been that of the causal relation of the mosquito to malaria. We have no primary malaria in New Zealand—i.e., none originating in New Zealand; but the subject is, especially at the present time, when so much rivalry exists among colonising nations, of the gravest concern to all engaged in the work of colonisation, or in that of carrying the benefits of civilisation or religion to those parts of the inhabited globe which have not yet come under their influence. It is of special concern to such civilised lands as India, Italy, and some parts of America, where malaria has to be reckoned with as a serious hindrance to the material prosperity of the country.

The importance of the discovery that mosquitos play a part in the dissemination of malaria can be realised only by those who have some knowledge of what a powerful influence that disease has had in retarding the settlement and development of new lands, or in the impoverishment of so rich and ancient a nation as Italy. To-day tropical Africa is still a comparatively unknown land, although European settlements have existed along the coasts for centuries. Exploration of the interior has been difficult; the opening of it to commerce and civilisation has proved a gigantic task, as yet hardly more than begun, mainly because of the malarial fevers which have been met with and which have so often either turned back the explorer or merchant or claimed him as their victim.

A similar story is to be traced in the history of the colonisation of twenty centuries and more ago. When the Greeks sought to found the colonies in northern Africa or southern Europe the fevers they met with were as formidable opponents as the inhabitants of the lands they wished to occupy. It is recorded of the foundation of Rome itself that its site was chosen because it was a healthy spot, although in the midst of a district where fevers were prevalent. When the Romans later carried their civilisation by force of arms westward and north ward the same fevers were to be feared and reckoned with.

More than once in comparatively recent history has an army returned vanquished, not by the foe it set forth to meet, but by malarial fevers. One memorable instance in the history of our own nation is the ill-fated Walcheren expedition; another the attack on the Spanish colonies of Central America, which ended in the disaster at Cartagena.

It is estimated that in India there die annually from fever (mostly malarial) five million people. Of our army there (including Europeans and natives) one-third suffer every year from malaria. The loss to individuals and to the nation from the incapacity thus occasioned cannot, of course, be accurately gauged, but can to some extent be understood from the immense death-rate just mentioned.

As regards Italy, an Italian writer of repute (Celli) states that the activity and progress which at the present time is so distinctive of northern Italy compared with the other parts of that country are in a large measure due to the absence of the fevers so frequent in the southern districts—the Roman States and Naples. A few years ago a society in Rome, having as its object the study of malaria, justified its foundation by stating that the disease prevented the cultivation of 5,000,000 acres of Italian soil, annually affected some two millions of its inhabitants, and killed about fifteen thousand.

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In some of the British colonies malaria has doubled the cost of government. During the year 1896 281/2 per cent of the Government servants on the Gold Coast had their services lost to the State through death or ill-health due to it. An old neighbour of our own, Sir William McGregor, at one time in Fiji, later Governor of New Guinea, and now of Lagos, has stated that the Town of Lagos needs only one thing to make it a great commercial centre, and that one desideratum is the control of malaria.

The presence of such a scourge has naturally incited attempts to prevent its occurrence. For centuries there has been a continued effort in this direction. The study of the disease from the point of view of those concerned with the care of the public health has at times been rewarded with partial success. Certain points in connection with its occurrence were early noted, more especially its prevalence in marshy or swampy places. As districts became better cultivated, and so better drained, the presence of intermittent fevers was less and less felt. We find that in early Roman times certain parts of the country around Rome were methodically drained by means of extensive and complicated systems of underground channels. These districts lost their then unhealthy character and became thriving and populous. Later, owing to civil war and consequent neglect of cultivation, the drains became obstructed and the unhealthy conditions returned. The populations of once thriving villages and farms was gradually reduced, and finally the few survivors fled to a less pestilential part of the country. Their dwellings now form some of the ruins of the Roman Campagna. Attempts to repopulate these districts were made from time to time, but were attended uniformly by failure.

Parts of England, also of France and Germany, have within comparatively modern times been very subject to malaria. The drainage of low-lying lands was, no doubt, the cause of its gradual extinction, an extinction, however, not entirely complete, for sporadic cases are met with now and again.

Although, however, it was recognised that the drainage and cultivation of swampy lands in some places played an important part in lessening the fever, the reason of this was not understood. In equally swampy districts no malaria at all was to be found. In other places where there were no-swamps and good cultivation it was prevalent. In some districts of India cultivation seemed rather to increase the unhealthiness of a place in regard to fever; but, then, the growing of rice necessitated the presence of surface water during certain seasons. It was evident that neither the state of cultivation nor the absence or presence of swampy lands were in themselves a full explanation of the absence or presence of malaria. We now know such influence as the drainage of the land had was due to the destruction of the breeding-places of mosquitos.

It was noted that very frequently the excavation of earth was followed by a sudden outbreak of malarial fever In Hongkong such an outbreak occurred on one occasion among the soldiery of an English regiment, near whose barracks some excavations were in progress. The same has frequently been noticed in other malarial countries where railway cuttings or similar works were in progress. The explanation is that these works cause the formation of irregularities in the surface of the ground, in which water collects and forms suitable breeding-places for the mosquitos. Until recently these incidents were regarded as evidence that the fever was due to “emanations” from the disturbed earth.

What has stood in the way of prevention has been that the essential cause of malaria has not been known. Speculations in regard to it had been very numerous, but no satisfactory explanation had been given; and, as is apt to be the case under such circumstances, the want of knowledge was cloaked by the use of vague terms expressing speculative theories as to the origin of the disease.

Malaria is known under many names; some, such as “ague” and “intermittent fever,” have been given from the symptoms the fever presents. “Malaria” itself is a term expressing merely the opinion that it arose from unhealthy air. Similarly we find the supposed cause named “marsh miasma” or “paludinism”; of later date is the term “telluric poison,” this term coined after its supposed connection with emanations from the soil was brought into prominence. So late as 1886 a standard text-book defines malaria as an “earth-born poison for the most part generated in soils the energies of which are not expended in the growth and sustenance of healthy vegetation.” Analysed, this very vague definition is only an evasion of a confession of ignorance. Under such circumstances there was little hope of coping

successfully with the disease. “So long as its cause was unknown the methods of treatment were empirical, and so long as there was no definite notion of the mode in which it was disseminated efforts to prevent it were imperfect and to a large extent futile.”

The same vagueness which until recently characterized our knowledge of malaria was characteristic also of many fevers, but the number of these has been much reduced during the latter half of the nineteenth century, owing to the birth of what is known as the “germ theory.” It was shown that some diseases were due to the presence in the body of certain small organisms or germs. The importance of this discovery was so great that, as is often the case under similar circumstances, there was a tendency to explain the origin of pretty well all diseases by the “germ theory.” Investigators setting to work at some disease with this as a working hypothesis easily persuaded themselves that some germ they had found was the cause of the disease. In some instances these discoveries were confirmed, but in numerous other cases it was shown that the enthusiasm of investigators had led them astray. Malaria was one of the diseases which certain observers were prepared to ascribe to bacilli they had discovered in malarial patients, but these observations were not confirmed.

There were so many false hopes raised in this way that the announcement of a new discovery of the kind was at last regarded with great suspicion, and when it was reported that a French military surgeon in Algiers, named Laverau, had found certain peculiar bodies present in the blood of malarial patients, and in the blood-cells of malarial patients alone, his opinion that they were the essential cause of malaria was not much regarded. His work, however, stood the test of time, and after many years was confirmed by other scientists, and received recognition at the hands of even those who had previously thought they had reason to think a bacillus responsible for the disease. These bodies found by Laverau were not bacteria. They were more closely allied to the group of low organisms called Coccidia. These bodies are very insignificant, but it was noticed that they underwent growth and other changes in the blood-cells, the last stage consisting in their rupture and the liberation of spores, which serve to begin another cycle. It is interesting to note that this cycle corresponds in length of time with the period from the beginning of one attack of fever until the beginning of the next. It was shown also that there were different varieties of parasite, some taking longer than others to go through the cycle. This corresponded with what was already known about malarial fever—that one kind took two days, another three, from the beginning of one attack to the beginning of another.

A practical result of this decision that parasitic bodies were the cause of malarial fever was investigation as to their origin, whence and how they reached the blood of man. This question baffled all observers for many years. The clue to its solution was given by the observation that some of the malarial parasites in specimens of blood examined some minutes after its removal from the body exhibited a change, in which processes (“flagella”) grew out from them, these processes finally separating from the parasites and moving off on their own account.

Now, some living creatures of a low order have the peculiarity that their life-cycle varies with their environment, and it was known that some organisms very similar to this protozoon of malaria developed under special circumstances just such moving bodies as these flagella as the first stage of a new cycle of development. This was suggestive. There must, of course, be some purpose served by these flagella, and that purpose apparently had nothing to do with the life of the parasite within the body of man, since their appearance was always subject to the removal of the parasites from the body. Granted so much, and it followed that the malarial parasite had a second life-cycle apart from man of which these flagella were a necessary phase. It was Dr. Manson who argued thus, and he went still further. He was of opinion that the only natural means by which the parasite and the blood containing them was likely to be removed from man was through the agency of some blood-sucking insect. He suggested the mosquito. He was biassed in favour of the mosquito, because he had already shown that it was the intermediate host of another human parasite, a minute worm called Filaria.

(I may state here that there was a long-standing tradition among the peasants of Italy that malaria and mosquitos were in some way connected; and among certain tribes in German East Africa not only is the same belief held, but the same word is used both for malaria and the mosquito.)

Manson suggested that when the mosquito had sucked malarial blood the parasites developed these flagella in the stomachs of the insects, and these moved off through the stomach-walls to other parts of their bodies, and then in some way, after further development, once more reached a human host. Manson suggested that the mosquito either died in water or that its body was washed or blown into water which was afterwards drunk by a man; but this part of his theory proved incorrect. Manson was in London himself, and had no opportunity of experimenting to test his theory, but his lectures made a great impression on an army surgeon named Ross, who had already done some

work on the subject. On his return to India Ross set to work at long and patient investigations which were finally crowned with success. He proved definitely that mosquitos were the carriers of malaria, and pointed out the way in which infection through them happened. Ross's full story, apart from his scientific work, has not yet been published, but enough is known of it to enable us to assert that it was only his indomitable perseverance in the face of many difficulties, if not actual opposition, which made success a possibility. The catching and dissection of insects is a hobby which even within walls devoted like our own to the furtherance of science does not always secure unstinted praise, and the catching and microscopic examination of mosquitos did not meet with the approval of Ross's immediate superiors. During the progress of his voluntary investigations he was for a time sent to a station where he had no opportunity of studying the subject. This fortunately was not until he had done sufficient to attract the attention of the scientific world.

Ross began his investigations by searching for the malarial parasite in mosquitos. To this end he examined many hundreds after they had fed on malarial blood. He found readily enough that the flagella developed in their stomachs, but he could not trace them further. By chance, however, he came across a few dappled-winged mosquitos of a kind different from those he had hitherto experimented with. Examining these a few days after they had fed on malarial blood, he noticed something which he had found in none of the other mosquitos. The walls of the stomach were studded with peculiar little saccular bodies, which contained a pigment very like that of the malarial parasite. These cells he noticed were capable of growth, since they enlarged from day to day. It was at this stage of his work that Ross was obliged to give it up on account of his transfer to another station. He had, however, created a good deal of interest in what he was doing; so much so that after a time he was relieved from military duty and sent to Calcutta to continue his investigations. Unfortunately, it was a time of year when little ague was to be met with, and he had difficulty in getting material to experiment with. In this dilemma he turned his attention to a form of malaria in birds. He found that certain species of mosquito fed on malarial sparrows showed growths in the walls of their stomachs very similar to those we have mentioned; but he went further. He bred young mosquitos from the larvæe, and when these were fed on malarial sparrows showed he found these growths in a large percentage of them. Of those fed on blood which was non-malarial none showed these growths in their stomachs. He found, indeed, that the number of growths was roughly proportional to the number of

parasites to be found in the blood on which the mosquitos had fed. This proved definitely that these pigmented cells were developed from the malarial parasite.

Light was thrown on the way in which the process of development occurs by an American observer, McCallum. He showed in another bird parasite that the purpose of the flagella was to-fertilise others of the parasite which did not form flagella. The flagella entered into these and mixed with their substance, which underwent certain changes, as a result of which the form altered into a somewhat conical body endued with power of locomotion and penetration. If the vermicule met with a blood-corpuscle it apparently bored right through it. These stages of development have since been shown actually to occur in connection with the malarial parasite of man, and it has been shown that it is a vermicular form which is able to penetrate the wall of the mosquito's stomach and there developes into these sac-like bodies.

Ross, then, had traced the malarial parasite of birds as far as the stomach-wall of the mosquito. His next observation was that some of the mosquitos, after several days, had scattered through them minute rod-like bodies. On pressing on some of the larger of the sac-like bodies, and thus causing their rupture, he found that innumerable rods of the same kind were liberated, and he concluded, therefore, that the bodies ruptured naturally, and their contents, these rods, were so liberated into the circulation of the mosquito. This the anatomy of an insect would readily permit. Ross showed it was so by pricking the back of a mosquito and examining the minute drop of blood thus obtained. It abounded in the rod-like bodies. In endeavouring to determine the function of these rods Ross came across a gland connected with the proboscis of the mosquito, in which the rods seem specially to collect; and not only did he find them in the gland, which was the salivary gland of the insect, but also in its duct, which opens through the proboscis. This salivary gland forms a fluid which is injected into the skin of the animal on which the mosquito feeds before it begins to suck. It is supposed that this saliva keeps the blood from clotting, and so aids the mosquito in getting a good meal. At all events, it was probable that when a mosquito containing these rods attacked an animal some of the rods were injected at the site of puncture. Ross accordingly allowed mosquitos which had had time to develope these rods to bite sparrows. These in due course developed malaria. Thus was established the proof that mosquitos play the part of an intermediary host for the malarial parasites of birds—in other words, that the mosquito carried the infection from bird to bird.

Ross published his discoveries at once, and forthwith many

corroborative experiments were made in different parts of the world. In Italy work undertaken to show that the same was true of human malaria was equally successful.

Ross had early found that it was not every kind of mosquito in which the malarial parasite could continue its development. It was now a practical question to decide what mosquitos were and what were not responsible for the conveyance of malarial infection. For this purpose a proper classification of mosquitos was necessary, and, curiously enough, the classification of these insects was found singularly deficient and confusing.

The term ‘mosquito” is itself an indefinite one. It is the diminutive of mosca, the Spanish word for fly. Applied by the Spaniards to certain troublesome insects, it was adopted into other languages, and came in time to include not only different species but also different genera. Most of them belong to the gnat family, or Culecida, and there is indeed very little, if any, difference except in name between many gnats found in temperate regions and mosquitos in tropical countries. I am using the term “mosquito “to-night in its widest sense.

The deficiency in the classification of mosquitos was soon overcome. The whole civilised world was more or less interested, and numerous observers in each country helped in the work. The British Museum authorities issued a pamphlet,. “How to collect Mosquitos,” and sent it to British officials throughout the world, both in British dominions and at consular agencies elsewhere, at the same time asking that specimens of species found might be forwarded to the Museum. In this way a large mass of valuable material was obtained, which aided materially in the classification and identification of the species responsible for the carriage of malaria.

Many different species were used to repeat Ross's experiment—i.e., that of raising mosquitos from larvée and letting them feed on malarial blood to see whether the malarial parasite would develope in their stomachs; but the same conclusion was come to all over the world—that it was only among the members of the genus Anopheles that this happened. Where human malaria existed Anopheles was always found, and, roughly speaking, the distribution of Anopheles over the globe corresponded with the distribution of malaria. The knowledge of the actual mosquito concerned being once attained, the experimental research in connection with the prevention of malaria was much facilitated.

There still remained many doubters of the truth of the discovery. In some high places in India ridicule was cast on the idea, and the ordinary lay mind was able to find many.

arguments (fallacious ones) against the theory of the implication of mosquitos as agents in the propagation of fever. For this the indefiniteness of the term “mosquito” was in large part responsible. The medical and lay press were inundated with letters, more especially from retired officials, who asserted that they had lived for years in mosquito-infested regions and had not had malaria. These individuals had not taken into consideration the fact that a special mosquito was required. Some asserted that malaria had arisen where no mosquitos were to be found, but in most of these instances a proper investigation led to the finding of Anopheles.

The occurrence of cases at sea was brought forward as another argument against the theory, but here the explanation was readily forthcoming. The period of development after the mosquito injects the parasite lasts some twelve to fourteen days, and the period allows the infected individual to travel a long distance. An instance of this occurred on a steamer which, after leaving Calcutta, anchored for a night in the delta of the Ganges. She called only at Colombo, and three or four days after leaving that port there was a general outbreak of ague. The time was about fourteen days from the Ganges, showing, as we now know, that the infection had taken place in that river.

Although the scientific proof of the mosquito theory was complete, something further was needed to impress the fact upon the mass of those living in malarious districts, and perhaps more especially on lay officials responsible for the sanitation of tropical colonies. To do this, experiments of a somewhat sensational character were carried out in several countries. I will refer only to those for which British workers were responsible. One of those experiments consisted in the rearing of Anopheles in Rome from the larvæ, and allowing the adult female mosquito thus reared to feed on a malarial patient in a Roman hospital. For the purpose a case of a mild type was chosen. The mosquitos thus fed were forwarded, carefully packed, to London, and allowed to have another meal from voluntary victims—medical men—one of whom was a son of Dr. Manson, the originator of the mosquito theory. These London volunteers in due course developed malaria of the same type as the patient in Rome who had afforded the mosquitos their first meal.

A second experiment was undertaken by some medical men connected with the London School of Tropical Medicine. Their ability to make it was largely due to the Colonial Secretary, Mr. Chamberlain, who appreciated its value in relation to colonial development. The experiment consisted in building a mosquito-proof house specially designed to be suitable for British officials in malarious countries, well ventilated,

but with windows and doors and other openings protected by mosquito-proof netting. This house was erected at Ostia, not far from Rome, at the mouth of the River Tiber, in a district so malarious that any one spending a night there at certain seasons was expected to take malaria. The place was chosen as one of two suggested by Roman observers as having the worst reputations for malaria. The house was inhabited by two medical men and their attendants. By day they went about exploring the country, studying the mosquito life of the district, or amusing themselves. At sundown, however, they went within-doors until after sunrise. The peasants of the neighbourhood considered them mad to come to such a place. Subsequently, when the strangers remained healthy while the peasants were attacked as usual by the fever, the latter came for medical treatment. The experiment lasted for three months (from June to September), and the experimenters remained well during that time. An unexpected addition to the experiment was made during their stay at Ostia. The land on which the house was built was part of a Royal hunting estate, and King Humbert, of Italy, took a considerable interest in the experiment. While it was in progress he was assassinated, and it came to the ears of the authorities in Rome that in Ostia were certain suspicious characters in communication with anarchists. To arrest these, sixteen police officers were sent down from Rome. They spent only part of one night in Ostia, but every one of them about a fortnight later developed malaria.

Similar experiments elsewhere proved equally successful. Dr. Grassi, of Rome, chose another notoriously malarious district, and protected there some of the houses of the railway workmen. Those whose work required their going out at night wore veils and gloves. There were 104 people in these houses. All of them remained free from malaria, although their neighbours, not protected, contracted fever as in other years.

It was thus shown that the individual could under certain circumstances be protected from the mosquito, and so from the malaria; but it was an impossible undertaking to protect all the houses and huts of a country, or keep all the inhabitants within-doors at night. It was desirable to find other means of prevention applicable over larger areas.

The dissemination of malaria theoretically might be stopped either by preventing the infection of the mosquito by man or by preventing the infection of man by the mosquito. The prevention of infection of mosquitos is to be attained by either curing all cases of malaria by the use of quinine or by keeping patients under such conditions that the mosquito could not reach them. In pre-

venting infection of man by the mosquito there are also two courses open—to destroy the mosquitos or protect the man. The possibility of the latter, the protection of the man, we have already shown. The destruction of the mosquito is a very big order, but when its life-history and habits are studied it is seen to be possible within limitations.

Let us for a moment consider the life-history of the mosquito. The great interest aroused by Ross's discovery has made our knowledge of the subject much greater and more exact. Different species have different habits, but there is a great deal common to all. The members of the family Culecida, to which both Culex (the common gnat) and Anopheles belong, pass, like other insects, through different stages of existence, presenting in these stages very different appearances and very different modes of life. From the eggs are hatched the larvée. These inhabit pools of water or the quiet edge of a slowly flowing stream. They feed on minute organisms growing in the water, on vegetable matter, also on each other and on the larvée of other insects. They require air, and come to the surface to breathe. After a time the larva sheds its outer coat and becomes the pupa, which also lives in the water but which, unless disturbed, rests quietly at the surface. If disturbed it jerks itself rapidly and forcibly to the bottom. After two or three days the pupa in its turn breaks open its outer skin and the adult mosquito emerges. Hitherto the insect has been aquatic in its habits; but the mosquito, after resting on the pupal skin through which it has broken until its wings are hardened, flies off to the nearest shelter, seeking in the day-time a retired dark spot, but issuing forth at night in search of food. Within a few minutes of sundown it goes abroad, and punctually just before sunrise seeks its hiding-place. (Hence the reason that malaria is contracted mostly at night, and an explanation of the fact that exposure to night air has been for ages regarded as a potent factor in the causation of malaria.) The mosquito feeds on various foods, sucking readily the juices of plants and fruits. It is only the females which are blood-suckers; the male is a vegetable feeder. As a result of observation and experiment, it is believed that the sucking of blood by the female is connected in some way with the proper development of her eggs. Only those mosquitos which have sucked blood produce fertile eggs. After gorging itself the female returns to cover. She does not fly far, and is not carried by the wind, for when the wind is strong the mosquito rests quietly. This fact explains why malaria is contracted often within a very limited area of a district or village. The mosquito does not travel beyond the immediate vicinity of its birthplace. Nor does it fly high in

the air. This fact explains the belief in many malarious countries that huts on high foundations are healthier than those built closer to the ground, and also the salubrity of villages built on hills rising above malarious plains, a well-known fact exemplified by a striking feature in many parts of Italy, where towns and villages are seen on the hills overlooking the level country, where most of the inhabitants ply their vocation as agriculturists.

Even so cursory a description of the life-history of mosquitos suggests several means of getting rid of them. Water exposed to air is required for the life of the larvæ; cover tanks or remove pools by efficient drainage and they cannot exist. A suggested method for use in cases where water cannot be removed, where the mosquitos breed in small lakes or on the banks of rivers, is to spray kerosene over the surface of the water. It spreads out in a film, very thin, but sufficient to prevent the larvæ obtaining air. The larvæ float on the surface with their breathing-tubes above in the air. The kerosene chokes them. The fact that the Anopheles lie quiet during the day in the interior of a house or hut enables them to be killed readily by various vapours. A dwelling can thus be freed from them, and may be kept free by the use of proper netting over doors and windows. These three methods—efficient drainage, the use of kerosene on the surface of pools to destroy the larvæ, and the killing of the adult by insecticide vapours—are the principal means to be depended on in the destruction of mosquitos.

We have noticed that it is possible to prevent the infection of mosquitos by destroying the malarial parasite in the human blood. This is done by the use of quinine. Where, however, the population is large, especially among uncivilised peoples, there are difficulties in the way of its employment. The expense would be greater than any Government could well afford. Moreover, natives do not care to take it—it is too unpleasant for them. Among native races also it is very difficult to decide, without examining the blood, which individuals are malarious and which are not. It has been shown in different parts of the world that many of the hosts of the malarial parasite give no outward sign of being ill. Long-continued exposure to the parasite seems to give an immunity from its most apparent evil effects. The children of native races in malarial districts are almost uniformly affected. This has been shown by the observations of a special German Commission which visited Java, New Guinea, and East Africa. Any one of these children may serve as a centre from which the disease may be carried. Hence it is important that Europeans living or travelling in malarious districts should not have his dwelling or pitch his camp in

the vicinity of a native settlement. He should, if possible, keep at night at a distance from them, and even then should take other measures for prevention of infection.

The destruction of mosquitos, the use of quinine, the protection afforded by the use of netting, are probably none of them by themselves sufficient or possible in a community of any size or over large areas of country. They have proved effective in small communities. One recorded instance is that of a previously very unhealthy island off the coast of Sardinia. Malaria was entirely prevented there during one summer.

Even if in large populous districts entire prevention of the disease is impossible, much can be done by the means we have mentioned to diminish its prevalence, and the more valuable lives may be efficiently protected.

There is no better test of the value of such proposals than their adoption on commercial principles. This has been done in Italy, where legislation has actually been attempted to make employers in malarious districts provide for their employees lodgings and suitable dwellings in which protection is afforded against mosquitos. The Adriatic Railway Company, which used to spend annually £42,000 on hospital treatment and medicine or loss of service through malaria, has determined to attempt prevention by similar means among its workmen. As regards the British Colonial Department, it is making an attempt, more especially on the west coast of Africa, to minimise the occurrence of intermittent fever. The towns have been cleaned out, roads and streets have been drained effectively, the collection of water in pools prevented, articles like old cans or broken bottles in which water might be retained have been removed, netting is provided for the doors and windows of official residences, and the use of quinine by those suffering from ague has been insisted upon. Above all, the natives are being taught that it is possible to avoid the disease by taking proper precautions. It is hoped that in this way the evil reputation of West Africa as “the white man's grave” may soon pass away.

It is easy to forecast that the comparative immunity from malaria thus insured to the explorer and merchant will materially aid in revolutionising the commerce of some parts of the world. The results of the discovery of the cause of the disease will be far-reaching. We have seen how, in the opinion of those able to speak with authority, the control of malaria is the one feature in the condition of tropical Africa which prevents the proper development of trade. We know that it was the lack of such control which prompted Britain to relinquish her