GASTRIC C,CA OF THE HETEROPTERA. 149 



gener, in den Darm hineingelangter Bakterien ; (d] in der Festi- 

 gung des Korpers gegen pathogene Bakterien und gegen Bak- 

 teriengifte." 



Similar experiments with the same end in view have been 

 carried out by Moro and by Mme. O. Metschnikoff on newly 

 hatched tadpoles, Moro working with Pelobates fuscus and Mme. 

 Metschnikoff with Rana temporaria. The results secured by 

 these two workers seem to point ,to some important digestive 

 function for the intestinal bacteria, although the results in 

 neither case appear so conclusive as those given by Schottelius 

 for his work \vith chicks. In the work of Metschnikoff, for 

 example, the nearly mature embryos were removed aseptically 

 from the gelatinous, enveloping layer and allowed to develop in 

 vessels of sterile water under aseptic conditions. Of forty-nine 

 tadpoles which survived the first few days of the experiment, 

 forty-two developed accidental contamination, and seven re- 

 mained sterile throughout the experiment. 



Although for some reason the mortality was much higher 

 among the non-sterile tadpoles, and although the sterile ones 

 actually lived longest, the development of the sterile ones was 

 much slower than that of the non-sterile, the minimum weight 

 and length of the non-sterile corresponding closely to the maxi- 

 mum of the sterile. These results, however, are regarded by 

 the author as sufficiently conclusive to warrant the assertion 

 that intestinal bacteria are necessary for life and development 

 of tadpoles. 



Cohendy, on the other hand, in duplicating the work of 

 Schottelius on sterile reared chicks secured results which he 

 regards as proving conclusively that bacteria are in no way 

 necessary to the normal development of the chicken; and he 

 accounts for the results of his experiments as contrasted with 

 those of Schottelius as being due to the superior technique which 

 he claims to have employed. In the course of this work he was 

 able to keep chicks under strictly aseptic conditions for a maxi- 

 mum of forty days during which time the animals developed 

 normally, there being no essential difference in growth and 

 metabolism betw r een the sterile chicks and those kept as a check, 

 and the sterile chicks when placed under natural conditions, after 



