Art. X.—Nature's Efforts at Sanitation.

By R. H. Makgill, M.D., D.P.H.

tions of filth and overpopulation prevail—as in Chinese cities 1—the penalty takes the form of such epidemics as typhus, plague, and cholera. In more civilised communities, where at least the grosser part of the filth is removed, there is still the punishment to meet the crime in the shape of tuberculosis and pneumonia. Even where science does its best to counter-act the law, and we have the best artificial sanitary efforts—good drainage, well-ventilated houses, and inoculation against disease—the law still asserts itself, and unnatural methods of life lead to nervous disorders, digestive troubles, and so forth.

It has often been said that the London “cockney” does not survive beyond the third generation, and doubtless there is some truth in this. The best text-book in which to study the working of these laws is the Registrar-General's annual report. Compare the death-rate for town and country and we find a progressive rise as the population grows denser. In 1895 the returns for Great Britain showed a death-rate of 12.7 per thousand of population, where there were 138 persons to the square mile; but it rose to 33 per thousand where the density was 19,000 per square mile. New Zealand had, in 1901, but 7.4 persons per square mile, yet the death-rate was 9.8 per thousand—not so much behind the English rural death-rate, and with only one twentieth of the density. Here is evidence of the working of the law against overcrowding in spite of all our efforts. Why in a new country like this, with the lessons learnt in older communities to benefit by, and with ample room at our disposal, our legislators should have seen fit to take the standard of overcrowded London and fix a scanty 150 square feet as the minimum space to be allowed per dwelling it is hard to say. Surely we could avoid the evils of overcrowding at this early stage in our history.

Dr. G. V. Poore, a most eminent sanitarian, in dealing with overcrowding, remarks, “We have long been accustomed to hear that our chief sanitary necessity is pure water. This would be quite true if we were fish. But it is obvious that the air we breathe is of greater importance than the water we drink, seeing we take a draught of air about twenty times a minute, while many of us do not take a draught of raw water from week's end to week's end.” Sunlight and fresh air are our greatest sanitary assets, and we should not despise them.

The consideration of Nature's methods leads us to such endless fields for study that I do not propose to-night to do more than discuss two important branches of the subject: First, the disposal of organic waste in Nature; secondly, the laws by which our bodies are protected against the inroads of infectious organisms.

Organic Waste.

There is a well-known saying that there is no waste in nature, and the truth of this is most strikingly observable in the constant circulation of organic matter. The relationship between animal and vegetable life is a simple illustration, the animal building up its body by means of the grass it eats, which building process is accompanied by a breaking-down or combustion, shown by the exhalations of carbonic acid and water in the breath, waste products of the vital process. The green leaves of plants absorb the carbonic acid, using the carbon and giving off the oxygen to aid in the further combustion, while the water is deposited as dew, to be absorbed by the rootlets. The plant utilises the waste products of animal life, and, building them up, furnishes a fresh supply of food.

The most interesting point is the circulation of nitrogen—the most important element in organic matter—for by following this up we learn about Nature's scavenging process, by which organic waste material is not only disposed of but re-utilised. Organic matter is a complex body, built up by vital processes of the elements, carbon, oxygen, hydrogen, nitrogen, and sulphur. These elements are too valuable to waste, and therefore when a plant or animal is dead the mass of organic matter becomes a potentiality for further life. But Nature does not seize on the dead body and hustle it down a sewer, to be deposited on the sea-beach, nor does she bury it in a hole so deep that it is not available for any purpose. Instead, the body lies on the surface of the ground, and an army of sanitary officials at once set to work to make use of the stored material. And things are so balanced that each, while unconsciously working out the general scheme for disposal and utilisation, is at the same time making his own livelihood in the process. The first of the scavenging party to appear is familiar and objectionable—the blow-fly and house-fly. They come to feed and lay their eggs, so that the young, when hatched, will be assured of a plentiful supply of food. It may be objected that the fly is a weak point in Nature's scheme, as it is certain it can carry infection from diseased matter. But in that scheme it is not intended that decaying matter be smeared round our dwellings, so giving the fly a chance to spread disease. Our sense of smell may be regarded as a sanitary precaution, warning us to avoid the close proximity of offensive things, just as it doubtless serves to guide the fly to his special form of food. As decomposition advances another set of scavengers appear—namely, varieties of beetles, who live on the fatty matters. The well-known burying beetle is a specially energetic member of this

group of workers. Later another variety of fly appears, which also feeds on the fatty matters; these are the small flies which we find in cheese. The next contingent are very minute insects—the mites—whose work tends to dry up and mummify the now highly decomposed body. This prepares it for a further set of mechanics, whose food is found in the dried skin and ligaments; these are certain moths and beetles. Finally a variety of beetle sets to work to utilise all the débris left by the other squad of scavengers, working it into the soil and tidying it all up. These insects appear in regular routine, and do the grosser part of the clearing process.

The Microbe.

But the principal force making for the reduction of the complex mass of material is the microbe. The process of putrefaction by which organic matter—animal or vegetable—is broken down and dissolved is produced by bacterial life. And we are entirely dependent on the bacteria for the conditions necessary for existence, for if they were absent organic matter would not decay, plants could not live, and food-supply would cease. These micro-organisms require for their life, moisture, certain salts, and nitrogen and carbon in some form, varying with the variety of the bacteria. One group derive their nitrogen and carbon from the breaking-down of already organized material, and others do so from the simplest elements, building them up into the complex materials of which their own bodies are composed. Thus it would not be supposed that distilled water contained the elements of life even for bacteria. Yet one variety will grow in it, deriving its nitrogen and carbon from impurities in the air, such as carbonic acid and ammonia. But it is the first or breaking-down group which causes decomposition. An important feature of this process is that the bacteria which cause disease and death do not themselves long survive the decay which then sets in. The putrefactive organisms are antagonistic to them, and in course of time they disappear. Doubtless some survive in a modified form when conditions are favourable, and lie dormant awaiting an opportunity to again assert themselves; but thorough exposure to air and light, combined with the antagonism of the putrefactive organisms, and those universally present in earth and water, serve to kill out most disease-producing germs.

Inquiring now as to the agency by which these bacteria produce their solvent effect, we find that the growth of bacteria is accompanied by the production of heat—as in a mass of wet hay—and of certain ferments, which are the active chemical agents. If we filter a fluid in which these germs are growing through porcelain we can separate the

atmosphere, and the infective organisms and the putrefactive ones have been displaced by the normal earth dwellers, the nitrifiers.

I should mention here two varieties of bacteria which also live in the earth, and have their influence on the nitrogen for plant-food. One, of these carries the reducing process too far, as it breaks up the nitrites into the simple elements and allows the nitrogen to escape back into the atmosphere, so that plants lose it. But there is the other variety, which reverses the process, taking up free nitrogen from the air and building it up into organic bodies. This form is found in the nodules which grow on the roots of leguminous plants, the nodules being formed by the germs in their growth. By thus utilising the atmospheric nitrogen these bacteria enable the legume to live in a poor soil, and the value of cropping with these plants is apparent, as by ploughing them in the soil is greatly enriched. This particular nitrogen-collecting bacterium can now be bought as a substance called “nitragen,” and sown on the land.

Disinfecting the Soil.

The last of the organized material to disappear is, of course, the bones in animals and the woody fibre in plants; but they, too, ultimately decay, and are dissolved and utilised by the soil. In the process of “humification”—as this action of the surface earth has been called—many earth insects and worms play the part of tillers by turning over the upper layers, passing it through their bodies, exposing fresh layers to the action of air and light, just as the farmer does with his plough, leaving it pulverised, oxidized, and enriched. When we realise how the rich upper layers of the soil teem with this useful insect and bacterial life we understand why it has been spoken of as the “living humus,” and we realise the importance of moisture and air, and how flooding with water may stop its vital processes—drowning it, as it were. In a deserted stockyard, tramped down and consolidated by the feet of cattle in wet weather and baked hard by the sun in dry, the air cannot penetrate the earth, and grass will not grow in spite of the presence of abundant manure. But in course of time the earth cracks by frost or drought, the worms begin to turn it over again, air enters, and the humifaction of the manure starts afresh.

Under Water.

In streams and ponds the same process of reduction of complex organic waste takes place. Other forms of bacterial life are at work dissolving it, and water-plants, such as cress, duckweed, seaweed, and so on, are ready to absorb the

of worms and insects, which work the substances into the earth; and, lastly, the nitrifying organisms, which form the simple salts and gases which the plants can take up to build once more the complicated organic tissue, so completing the cycle.

We Should Imitate Nature.

I have given but a brief outline of the process, which, if followed out in its entirety, would occupy a great deal of time. Many important questions remain undecided. But at least we know sufficient of the general plan Nature follows to be able, if we are alive to our duties, to copy it in our own sanitary arrangements. We cannot, I fear, do this on the same economic lines, for, however much in theory we can deplore the massing of our population in towns and cities, it is the inevitable result of civilisation, and we must face the problem of dealing with accumulations of filth which Nature never intended should exist.

Dr. Poore, whom I have already quoted, is rather an idealist in his advocacy of trusting entirely to the humus, placing all our waste on the land. He rightly considers that drainage schemes favour overcrowding, which is at the root of most sanitary sins. He has for many years at his country house in England demonstrated what may be done in a carefully tilled garden in the way of refuse disposal. In the centre of the garden is a shallow surface well, in which, owing to its carefully constructed cement walls and covering, pure water is obtained, in spite of the quantities of filth dug into the soil round about it. This is all very well when some one is in charge who can take a scientific interest in doing the work as it should be done; but I fear the result of intrusting it to the care of the population at large would be disastrous. Moreover, in few towns do even the larger houses possess sufficient land for the purpose. We must remember that, however perfect the earth may be as a filter, it will not stand overwork any more than any other form of apparatus. If we heap 2 ft. of manure on a soil having only 2 in. of humus we must not be surprised if the result is offensive. The ground will deal with a certain amount of organic matter, but it must be given a fair time in which to act. Overtax it and there will remain an amount of undecayed organic matter which will be carried by the rain either down through the subsoil to our well or washed over the surface to our streams, causing pollution. We have, therefore, to look to drainage schemes and systematic removal of filth to preserve the balance of health. The worst thing we can do with such substances is, as pointed out by Dr. Poore, to carry it past our humus

purifier by means of drain-pipes and leave it unchanged on our sea-beaches or in our streams to putrefy and pollute the neighbourhood.

How Towns should be Dealt With.

In towns the pipes have to be used, however, and it is at the outfall of the sewers that we should provide systems of treatment which, in a measure, follow Nature's methods, and utilise, or at least render innocuous, the accumulated filth. There is a necessity in all such systems for keeping separate the sewage proper—that is, the waste from domestic and trade processes—from the storm-waters and natural streams. If we let them mix we have too large a volume of fluid to deal with, while at the same time the sewage is not sufficiently diluted to prevent its becoming dangerous and offensive. Unpolluted storm-water can be readily disposed of, while the sewage proper, being moderate in amount, can be submitted to any of the treatment processes which now form an essential part of all modern drainage schemes. Chief among such processes are the sewage farm, the chemical treatment, and the septic tank, or biological system.

It must be admitted with regret, as the Royal Commission on River Pollution long ago pointed out, that the sewage of towns must be treated as a nuisance to be got rid of in the cheapest and most efficient way, but must not be regarded as a source of profit. We cannot copy Nature's perfect economy when we break her rules to the extent of huddling together in large communities.

The sewage farm, to be a success, requires a large area of ground and a soil specially adapted as regards its porosity, and so on, and, though it is closely allied to natural principles, we have a difficulty in preventing our humus from being drowned unless a very large area of land be available. Thus it has been calculated that London's sewage would require a farm of 100 square miles. The chemical process is costly, and at best does not produce a very good effluent, while a difficulty remains in the disposal of the sludge, the precipitated organic matters. In the septic tank, however, every advantage is taken of the forces of Nature, the principle being to utilise the two great bacterial actions—first, the solution of organic matters, which we have seen in the decomposing body; and, second, the nitrification of the dissolved products, which we know takes place in the earth. The result is an effluent of clear fluid without smell or offence, a mere solution of nitrates and other simple salts.

Many forms of apparatus have been constructed which work on this principle, all nearly equal in efficiency. Advan-

tage is taken in this system of the fact that certain very powerful liquefying organisms only exist and act in the absence of air. For this reason the tank is closed hermetically, and the inflow and outflow pipes dip under the fluid-level and prevent ingress of air. All organic solids are liquefied in this chamber. The nitrifying organisms soon grow in the filter-beds, which are freely exposed, and the solution of ammoniacal and reduced organic products is nitrified and oxidized in the passage through the coke. When possible the effluent can be applied with advantage to the land, as it is rich in nitrates and other useful manurial salts. But if land is not available it can flow into the sea or stream without fear of offence.

Here, then, we use Nature's own processes, chained up, as it were, and working for us at our bidding, and as a result we have in this system the nearest approach to perfection yet attained in sewage treatment.

Protection.

I must now briefly mention another law by which Nature protects the public health, a law which is of interest from the fact that it is at work in our own bodies, enabling us to fight against the inroads of disease germs. There is a natural resistance of the living body against organisms which attack it. The living animal cell and the disease germ or pathogenic, bacterium are engaged in a continual warfare. Probably the general health of the body has much influence on the question of which way the warfare will end, since we know that influences tending to depress the general health also tend to lay the body open to attack by such infective organisms. We know, for instance, that persons living in unwholesome surroundings are more liable to attacks of typhoid fever than those whose environment is sanitary, and this has been demonstrated experimentally with guinea-pigs. Anything tending to depress the vitality of the living cell favours the infective germ by lessening the resistance.

But Nature has another beautiful law of compensation, a law by which she makes the very life of the germ prove antagonistic to itself. It is the law which confers on us immunity from second attacks of an infectious disease. We all know that second attacks of scarlet fever, typhoid, smallpox, and so on, are rare. If it were not so, if there were no such thing as acquired immunity from such diseases, and we were to catch them as frequently as we catch cold, life would be a pretty serious matter. The secret of how Nature works this law has been an object of speculation with scientists for a long time, and we are now beginning to have some glimmering of light on the subject.

Infection occurs if the germs of disease can—(1) Live and increase in the body; (2) produce their injurious substances. It is these injurious substances, called “toxins,” which produce the symptoms of disease. This we know, because we can grow in the laboratory a culture of a disease germ—say, typhoid—in broth. Then by filtering through porcelain we rid it of the actual bacteria, and yet the symptoms of the disease can be produced if we inject the germ-free broth. But if we make our culture in the living body, as it were, by infecting an animal, we can also demonstrate the formation in the blood of substances which act antagonistically to the germs and their poisons.

Natural Immunity.

Immunity, or the power to combat disease, can be divided into two lines of resistance—(1) Natural immunity; (2) acquired. Natural immunity, the first line of resistance, is shown in certain animals which do not take special diseases. Thus cattle cannot be infected with glanders, a disease of the horse. Man does not take rinderpest, and so on. The reason for this immunity is probably merely an extension of the natural resistance all living bodies have against infection. The white corpuscles of the blood are called “phagocytes,” because they eat up germs, as we can demonstrate under the microscope. Probably they secrete a sort of poison to germs, killing them first.

Guinea-pigs do not naturally suffer from typhoid, yet, as I mentioned before, by keeping them artificially in depressing conditions we can lessen their resistance until they can be infected. Certain individuals possess naturally in their blood a strong resistant power to diphtheria, so that their blood will kill such germs when we mix them together, a power not possessed, unfortunately, by all of us. This is an instance of an unusual development of the first line of resistance. Natural immunity is a subject about which we know as yet very little.

Acquired Immunity.

Acquired immunity is the second line, and this is attained—(1) As an after-result of the ordinary course of infectious disease, so that we do not suffer repeated attacks; (2) by artificially inoculating into the body cultures of the true or allied organisms, which in some way are rendered less virulent than normal, as in vaccination; or, again, by injecting the poisonous products of such organisms in such small doses that they do not injure us. Yet they cause a reaction in the body, leading to immunity from the disease they themselves cause.