Transmission 13 



eggs which have left the preceding host with the urine or the fseces. 

 The only medium in which they find the condition for further 

 development outside man is water." "Authors have tried to find 

 a mollusc capable of rearing the germs of Bilharzia ; I have person- 

 ally experimented with all the species occurring in the Nile Valley, 

 but in vain. I equally failed with larvae of insects living in water, 

 with various species offish, with plants, etc. In such circumstances 

 the only alternative left was to assume that the germs from the 

 water immediately return into man, making their way to the liver, 

 w^here they reproduce the Bilharzia worms." 



During 1911-13 Japanese investigators had succeeded in infect- 

 ing cattle, cats, and dogs with an allied disease, caused by 

 Schistosoma japonicum, by immersing the animals in the flooded 

 fields of infected areas, but had quite failed to obtain infection 

 by similar immersion in water containing large numbers of live 

 miracidia. Commenting upon this in 1914, Dr. Looss [300] says: — 



" Merkwiu-dig ist dass die japanischen Autoren anscheinend zu 

 keiner Klarheit iiber die Natur der Invasionsform kommen konnen." 

 " Nach [Miyawa] zeigt die Invasionsform einen so betriichtlichen 

 Unterschied " von dam Mirazidium, dass die Existenz eines Zwisclien- 

 wirtes wahrscheinlich wird. Ist dies richtig, daun miisste sich B.japonica 

 in ihrer Entwicklung weseutlich von B. hcematobia unterscheiden, denn 

 wie ein im Wasser lebender Zwischenwirt an der Verbeitung der letzteren 

 in dea Stadten yEgyptens befceiligt sein soil, scheint zunachst schwer 

 verstandlich." 



It is remarkable that the Japanese authors do not appear to be able to come to 

 any clear concept as to the nature of the invading form. According to Mij-awa, the 

 invading form manifests such marked divergences from the miracidium, that the 

 existence of an intermediate host seems probable. If this statement is correct,' 

 Bilharzia japonica muat differ essentially in its development from B. hcematobia, for 

 it seems a p-iorj difficult to understand how an intermediate host that lives in water 

 can participate in the spread of B. hcEmatohia in the tovirns in Egypt. 



Direct The earliest attempts to obtain direct infection 



Infection experimentally were made by Harley [216] in 1871. 

 ExPEBiMENTs. <. ^^^ ^^^^^^ rabbits and two dogs were allowed 

 to take, at intervals with their food, pellets of the mucus containing 

 swarms of the eggs. Three of these animals were killed after an 

 interval of two, three, and six months respectively, and carefully 

 examined, but no trace of Bilharzia could be found." 



Mantey is reported to have made some experiments in 1880, 

 but his account [331] has not been accessible. The results are 

 quoted by Looss as having been negative. Lortet and Vialleton 



This has been experimentally demonstrated by Miyairi and by Leiper and Atkinson. 



