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Discussion.
The species recorded above possess in common the direct type of life-history. Involving only a single host, auto-infection is a possibility and a contributing factor in the maintenance of untreated infestations throughout long periods in the life of the host. Such sustained infestations survive long journeys and distance is no barrier in the dispersal of these entozoa, which are now cosmopolitan. On the other hand, in the absence of such complications as intermediate obligatory hosts and of free extra-human existence, these entozoa perform their simple life-histories independent of climatic conditions and influenced principally by the sanitary conditions and behaviour of the host.
The 100 individuals examined have been assigned to the categories of faulty or faulty at times, and normal with regard to their personal hygiene. The selection for examination was made at random, and has produced a group of forty-four individuals in the first category, and fifty-six in the second. The groups are not fully equivalent. The normal group is more heavily weighted in the age range of twenty to fifty years which includes forty-one individuals, contrasted with the faulty group which has only eighteen individuals in the same age range. Meleney, Bishop and Leathers (1932) have demonstrated the correlations of age and incidence of entozoan infestations, and the more even distribution of individuals by age in the faulty category might be expected to limit the comparison of the two lots; but such restrictions are greatly curtailed by the auto-infective nature of the organisms, the implications of breaks in personal hygiene, and other factors discussed later.
The data presented above serve to demonstrate the similarity between the entozoal fauna of the group studied and that of the same type of communities in other parts of the world. The occurrence of entozoa in 70 per-cent. of the persons examined by us is quite comparable with the findings of Boeck and Stiles (1923), who reported that 79 per cent. of a group of 505 persons, inmates of a mental hospital in the District of Washington, were infested with entozoa, although it is less than that reported by Young and Ham (1941), who examined a select group of 142 persons of untidy habits and found 90 per cent. infested. Infestations with protozoa, alone and in combination with helminths, were detected in 55 per cent. of the persons examined in the present study. This figure agrees well with the protozoan incidence of 52.15 per cent. reported by Bach (1932) from the examination of inmates of a mental hospital in north-west Germany. It indicates a situation similar to that of the 65 per cent. infestation by protozoa reported by Young and Ham (1941); but where the latter found 82 per cent. of the persons
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in the selected group which they studied positive for helminths, we have been able to determine only a 30 per cent. incidence of helminths in the whole group, a figure which is low and even low in comparison with this when the faulty group in which we found 50 per cent. positive for helminths is considered alone. This is quite likely a consequence of the simple direct technique which we have employed as a basic routine without recourse to concentration techniques.
The iodine-stained wet-preparation employed in the present work has been adopted as the standard on the basis of its broad general utility. The use of stained films, concentration techniques and other aids to greater efficiency in the determination of entozoa are not generally applicable with varying conditions of material or working quarters. The present technique can be employed equally on preserved or fresh material with a fairly constant relative efficiency. Accordingly, this technique has been chosen as the basic routine, although as shown by Faust and his associates (1939) in their studies on the comparative efficiency of various techniques, the saline and iodine wet-preparations have an efficiency of only 41 per cent. for entozoa generally, and detect only 33 per cent. of E. histolytica, 55 per cent. of E. coli, 62 per cent. of G. intestinalis, 6 per cent. of T. trichiura, etc., when two cover-slips are examined and ten minutes allowed for the examination. It is apparent from the incidence recorded for the several species determined by us that we have been able to achieve a better efficiency with this technique. This is the result of the considerable period of time allotted to the examination of each sample.
Comparison between the infestations of the normal and of the faulty groups is of particular interest. We have been unable to find, in previous accounts, any distinction drawn between the infestations observed in various groups in mental hospitals. In the present work, the total infestation by protozoa, including all records of infestations both alone and in combination with helminths, is closely similar for the two groups, the incidence being 54.4 per cent. for the forty-four members of the faulty group, and 55.4 per cent. for the fifty-six members of the normal group. The total helminth incidence is in striking contrast to this. Infestations with helminths were recorded in 50 per cent. of the members of the faulty group, alone and in combination with protozoa, while only 14.2 per cent. of the members of the normal group were positive for helminths. Clearly in these figures there is a relationship between personal cleanliness and helminth infestation; but equally clearly, the incidences recorded reveal no correlation between personal behaviour and protozoan infestation. There is a strong indication in these figures that although the life-cycles of these entozoa have a common pattern, a factor is operating which enables the protozoa to achieve more successes than do the helminths. There is, of course, the possibility that helminth infestations run their course more rapidly than do protozoan, but it seems unlikely that this has brought about the present situation in view of the persistent possibilities for reinfestation. It seems more probable that some route is open for the dissemination of protozoa, but closed to the helminths.
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Infested food-handlers have been commonly considered as potential factors in the distribution of protozoa. Sapero and Johnson (1939) have pointed out in this connection that they have been unable to determine significant differences between the incidence of E. histolytica in groups which contact, and others which do not contact food-handling carriers of this entozoan, nor does the food-handler seem a likely element in this case unless negative for helminths. The possibility of dust-borne infestations has been shown by Porter (1928), and of water-borne infestations by several workers (e.g. Hardy and Specter, 1935). Both of these routes would serve as a common entry to the whole community, but are also available for helminths, as has been shown by Porter, by Nolan and Reardon (1939), and others. In explanation of this common incidence in the two groups it seems necessary to assume some factor of a nonpersonal nature freely favouring the dissemination of protozoa but unsuitable for the transmission of helminths. The insect vector suits these three primary requirements. It has strictly limited powers to tranmit helminth infestations by external carriage; but possesses, as shown by Frye and Meleney (1932) and reaffirmed by Pipkin (1942), definite ability to transmit protozoan infestations by both external and internal carriage. At this stage we feel unable to do more than indicate the nature of the problem.