March 12, 1908J 



jVA rURE 



441 



destruction of crocodiles is a comparatively easy 

 matter, as the egj^s, sixty or seventy, can be collected 

 from the nests, the sites of which are well known 

 to the native. Possibly, however, aquatic birds 

 would still furnish them with blood. The dur- 

 ation of their life, their breeding habits, the 

 Habits of diflerent species, the conditions which give 

 rise to " lly belts," are almost unknown. It is some- 

 what remarkable that so little is known, although 

 many expeditions have now studied sleeping sickness ; 

 ihc Hy, however, has surelv been somewhat neglected. 

 One fact of great practical importance has, however, 

 become clear, vi/. that clearing the jungle drives 

 away the fly, and to this wc shall return. When we 

 consider next the mode by which the fly transmits the 

 disease, we find ourselves in the midst of controversy. 



One view is that the transmission is a mechanical 

 one, i.e. the fly carries infection as an inoculating 

 needle from one animal to another, and the known 

 experimental facts entirely support this view; and, 

 further, we have the fact that in Dourine this is the 

 sole (?also by fleas) known method, the mechanical 

 transmission being in this case by se.xual intercourse, 

 a method which, according to Koch, also takes place 

 to some extent in sleeping sickness. Another view, 

 that a deveIopment.il cycle goes on in the fly, is based 

 mainly on analogy and on the alleged existence of 

 sexual forms of trypanosomes in the blood, and more 

 ■ specially in the gut, of flies. VVe will not enter here 

 into the wilderness of arguments, but point out the 

 following facts. The tsetses used for experimental 

 purposes have hitherto, almost without exception, been 

 caught in nature, consequently, ex hypothesi, some of 

 them must contain the trypanosome in the required 

 hypothetical developmental stage. These flies have 

 then been fed on infected animals, and it was found 

 that when now fed on fresh animals the latter only 

 became eventually infected if the period that elapsed 

 since the last feeding on infected animals was not 

 longer than forty-eight hours, a fact explained on the 

 mechanical view by the statement that after this time 

 no longer can trypanosomes be found in the proboscis. 

 Now, if these flies, on the contrary, contained a 

 developmental stage of trypanosome, this result is in- 

 explicable except on one hypothesis, viz. that during 

 the feeding on infected animals (an unnecessarv pro- 

 cedure on this view) the flies completelv get rid of all 

 trypanosomes in the necessary developmental stages in 

 their salivary gl.-mds ( ?) by the preliminarv feeding on 

 the infected aninial>. This objection could be met bv 

 keeping flies caught in nature for fortv-eight hours 

 more or less. If now they are capable of infecting 

 fresh animals it would be in favour of the develop- 

 mental view and against the mechanical one; if not 

 capable of infecting it would negative the develop- 

 mental view, provided, of course, sufificient experiments 

 were made to allow for experimental error, &c. 



We might point out in this connection a possible 

 explanation of the difficulties encountered bv some 

 observers in obtaining positive results in transmission 

 experiments. In the case of anophelines caught 

 actually in native huts where the inmates were highly 

 infected with malaria, we have ourselves in certain 

 instances found only 3 per cent, of the anophelines 

 infected with parasites, a remarkablv low figure. Had 

 (hese anophelines been caught in cow-houses, where 

 (hey often abound, we consider that it would have 

 been possible to dissect thousands and find none 

 infected. Now, in the case of tsetse-flies, thev are 

 not found in houses, but live in the open, so that 

 u^les^ the flies have bitten man thev will not become 

 infected with the trypanosome (unless, indeed, thev 

 have bitten some other unknown host), .and if 

 the flies used in these experiments are collected from 

 parts of the bush where they have not bitten man 

 NO. 2002, VOL. 77I 



(or other host of the trvpanosome), it would be quite 

 conceivable that thousands of flies might be used in 

 transmission experiments with negative result, and 

 even if they had an opportunitv of biting man it is 

 still conceivable that the number of infected ones 

 might be very small if we consider the fact of the 

 low figure of 3 per cent, for infected anophelines 

 found by us in certain highly malarious districts. 



If we consider the matter from another standpoint 

 we see that again our knowledge is wanting. What 

 is the source of the T. gambieiisc':' Is it purely a 

 man-to-man infection, as we believe to be the case in 

 malaria, or can the fly convey the trypanosome to 

 man from various animals? This would seem to be 

 likely, for experimentally the fly has been proved to 

 transmit to monkeys, so that there seems to be no 

 a priori reason against thinking that the flies can 

 transmit not only from man to man, but from man to 

 animals and from animals to man. If this is so (but 

 arguments can be brought against this view), then it 

 has an important bearing on the results of isolation 

 of the sick, for the remaining healthy population mav 

 be still living amidst infected animals, domestic and 

 wild. 



In cattle in the Congo, in sleeping-sickness areas, it 

 is believed that the trypanosome is a different one, 

 viz. T. dimorphon. Even if other reservoirs of 7'. 

 gambiense exist, it must be admitted that the removal 

 of the sick would remove one important source of 

 infection, whatever proportion these bear to other 

 reservoirs (if existent) of T. -ganibiense. 



We should consider, then, that this is perhaps the 

 most important point which requires immediate solu- 

 tion, and it can be determined only by a long series 

 of laboratory inoculations. 



.A further point for decision, as we have seen, is the 

 mode of transmission, mechanical or developmental, or 

 both. This, perhaps, is of scientific rather than of 

 immediate practical importance. Thirdly, we require 

 a careful extended study of the habits of the fly. 



But although much investigation remains to be 

 done, we may now briefly recount what is being 

 carried out in the light of our present knowledge. 



Sleeping sickness can be detected in its earlv 

 stages, first, by the enlargement of glands, e.g. 

 those in the neck, an almost constant phenomenon 

 (and the glands on puncture show trypanosomes) ; 

 and, secondly, bv the method recentlv used by Koch 

 of examining fairly thick stained blood films on 

 several occasions. We have thus means at our dis- 

 posal of detecting early cases even when the person 

 is to all outward .tppearances healthv. 



(i) Isolation. — The removal of infected persons so 

 far as possib'e to localities free from the fly, where 

 they may be suitably treated, is certainlv imperative. 



(2) Inspection posts. — The spread of the disease to 

 non-infected areas where the fly exists by means of 

 infected persons should be controlled jo far as possible 

 by medical examination at inspection posts along the 

 main routes of traffic. Although no doubt some will 

 escape detection, yet the method is one which enables 

 us largely to control the spread of the disease. 



(3) Treatrwnt of the sick. — We have in atoxyl an 

 arsenic compound first introduced by Thomas and 

 Breinl, undoubtedly the best drug hitherto used, in 

 combating the disease. Undoubtedly cases of sleep- 

 ing sickness in Europeans have been cured by it, and 

 lately Koch, in an extended trial of the dru.g, has 

 spoken in laudatory terms of its use. He recom- 

 mends the giving of half-gram doses on two consecu- 

 tive days at intervals of ten days, and continuing 

 the treatment for long periods. The method is 

 slightlv different from that advocated bv the Liver- 

 pool School of Tropical .Medicine when it first dis- 

 tributed atoxyl throughout the Congo, but Koch has 



