PrerioKs WorJi on B. japonica 136 



stage coiilil he (|uickly and accurately delimited in the molluscs of a heavily 

 infected locality. By its use the peculiar difficulties which have so long 

 beset the bilharzia problem in Egypt were speedily overcome. 



Before dealing with these investigations, 1 must recall that the problem 

 of the bilharzia worms was not one of a peculiar and new type of larval 

 development. It concerned rather the seat of this development and the 

 exact route by which reinfection of man took place. 



Holders of the theory of direct transmission were in agreement with 

 their opponents that the larval metamorphosis of the bilharzia worms 

 conformed, in all essentials, to that of other digenetic trematodes. Thus 

 Looss, in 1908, wrote : " The existence of these (germinal) cells in the 

 bilharzia miracidium is absolute evidence that the miracidium cannot 

 develop directly into an adult worm, but must pass through the stage of 

 the sporocyst which in its turn produces, either and probably at once, or 

 by one or more intermediate generations, the definite worms." 



The fundamental problems for each species of bilharzia worm were 

 these : (1) Did the species follow its typical larval development in the liver 

 of man or of a mollusc '? (2) Did infection take place through the skin or 

 by the mouth '? (3) If a mollusc was an essential intermediary, what were 

 the species concerned in the transmission of each species of worm ? 

 As regards the B. japonica, the first and second of these problems were, 

 to my mind, conclusively settled by the researches of Fujinami and 

 Nakamura in 1908. 



In those regions in the Far East where man is infected with B. japonica, 

 infections also occur naturally in cattle, cats and dogs. Using these 

 animals therefore, as tests and controls, the following experiments were 

 made. In the first investigation numerous miracidia were hatched in 

 water. Dogs were then immersed in this. No results followed. In the 

 second series, cattle, cats and dogs were submitted to possible infection 

 by immersion in rice-fields and neighbouring ditches and streams reputed 

 to be sources of infection. Intense infections with B. japonica ensued. 



In 1910 other animals, not found naturally infected, were proved 

 susceptible by experimental immersion, viz., mice, white rats, guinea-pigs, 

 rabbits and monkeys. 



In these experiments, described by Fujinami in a paper issued from the 

 Internationale Hygiene Ausstellung in Dresden, in 1911, young parasites 

 only 015 millimetre long were found in the portal system on the third 

 day after immersion. 



In 1911 Miyagawa described the invasion forms, as seen in the 

 peripheral vessels and cutaneous tissues in two to twenty-four hours after 

 immersion. These forms were smaller than those seen by Fujinami but 

 differed in no essential respect. Oral and ventral suckers and a gut were 

 already present. 



In 1913 Miyairi, by experimentally infecting local molluscs with 

 miracidia, found a sporocyst in an unidentified snail, stated to be a 



