Travmiission 15 



bathing is, in this neighbourhood, at any,, rate, the most fruitful 

 source of the infection. I cannot, among several hundred instances, 

 recall one exception to^the rule that all who suffer from the parasite 

 have been in the habit of bathing. Moreover, it is among boys, who 

 are fondest of swimming, that the symptoms earliest make then- 

 appearance ; and I believe it would be hard, if not hnpossible, to 

 find one boy much given to bathing in the streams, or their tribu- 

 taries, who does not, before reaching manhood, become a subject of 

 the disease. Only on this theory is explicable the fact noted by 

 various observers in South Africa that the female sex is rarely 

 attacked by Bilharzia. 



" That the drinking of impure water is a common factor m the 

 process of infection there is no lack of evidence ; indeed, it would 

 be unreasonable to think otherwise if the bathing hypothesis be 

 well grounded. But, other things being equal, the chances of 

 infection occurring will be greater from the large quantity of water 

 which must come in contact with the body in bathing, than from 

 the comparatively small amount conveyed into the stomach by 

 drinking ; so that, granting the larvfe. to have the power of pene- 

 trating the body by some means, we should expect to meet with 

 a much larger proportion of cases among ])athers than among those 

 who only drink the infective water. 



"There is no evidence whatever that infection can take place 

 by direct contagion. The question of how infection occurs will, 

 however, only be satisfactorily solved when we have succeeded in 

 tracing the development of the parasite. through all its stages." 



It was in an article (1894) criticizing this paper that Looss, 

 while adopting the view taken therein that infection occurs through 

 the skin, first maintained, on biological grounds, that the infective 

 agent was the miracidium ['288] . 



The biological facts upon which he based this deduction were 

 explained by Looss [294] to the Egyptian Medical Congress in 

 1905, "il me sembla important de savoir si les embryons pouvaient, 

 oui ou non, resister a I'influence des acides de I'estomac. J'ajoutai 

 sur un porte-objet, au bord d'une goutte d'eau contenant quelques 

 embryons vivants, un petit morceau de la muqueuse stomacale d'un 

 singe recemment sacrifie et le comprimai legerement pour en faire 

 sortir quelque peu de sue. Des que les embryons arrivaient a 

 proximite de cette partie de la goutte, leurs inouvements cessaient 

 presque instantanement. J'ai, plus tard, repete ces experiences 

 avec un acide dont je connaissais la concentration. Une douzaine 

 de larves, a peu pres, ayant ete recueilhes dans un petit verre de 



