76 SOME MINUTE ANIMAL PARASITES 



infected with Spirochata balbianii, have themselves 

 become infected in the course of a few days, as have 

 also clean Tapes placed with infected ones. Similar 

 experiments, using Ostrea edulis, Pecten jacobaus, and 

 Tapes aureus, had similar results, showing that the 

 spirochaetes of these three hosts are, in the end, one 

 and the same organism. Sph&rivm corneum has been 

 cross-infected from Anodonta cygnea, though with 

 greater difficulty. Water in the aquaria in which 

 infected molluscs had been kept usually yielded 

 spirochaetes identical in every particular with those 

 in their mantle cavities or intestinal tracts. No 

 intermediate animal host is necessary for the trans- 

 ference of molluscan spirochaetes from host to host, 

 that function being accomplished by the surrounding 

 medium. 



Both oysters and mussels harbour certain com- 

 mensals, but so far none of these organisms have 

 been definitely proved to act as agents in transferring 

 spirochaetes from host to host. It is true that one 

 of us (1911) has found spores or bodies strongly 

 resembling them in the small A tax bonzi which 

 frequent the mantle cavity of Anodonta cygnea, and 

 that some of these bodies become rodlike; but we 

 maintain the attitude adopted two years ago, that 

 " as the complete metamorphosis of them into spiro- 

 chaetes has not been observed, it is well for the 

 present to consider them as being under suspicion of 

 being evolutionary stages of Spirochceta anodontce, 

 though they might be separate bodies." 



Turning our attention now to the blood-inhabiting 

 spirochaetes, it will be found that spore formation, 



