INFECTIONS OF THE DIGESTIVE TRACT 3 



tract. Even in temperate regions there are animals 

 whose alimentary tracts are comparatively free from 

 bacterial life. This is said to be the case with the parrot. 

 Other observers have, however, reached a different con- 

 clusion from that of Nuttall and Thierfelder. Schot- 

 telius * found that chickens fed on sterile food were re- 

 tarded in development and showed normal growth only 

 when given food containing bacteria. Similar results 

 were obtained by Madam Metchnikoff 2 in experiments 

 on tadpoles. Very carefully conducted experiments by 

 Moro 3 on the larvse of the turtle (Pelobates fureus, 

 Wagler) lead to the same conclusion; namely, that 

 intestinal bacteria are necessary to normal nutrition. 



It must be admitted, I think, that none of these ex- 

 perimental studies are really conclusive as to the neces- 

 sity of bacterial action in the digestive tract for the 

 maintenance of health in adult mammals of the highest 

 type man and various domestic animals. Experi- 

 ments on tadpoles and chickens cannot with confidence 

 be applied to the case of man. The experiments on 

 guinea-pigs can more justly perhaps be taken as typical 

 for mammals, but as the experiments of Nuttall and 

 Thierfelder were extended over only a short period of 

 time, they can hardly be held to prove that bacteria are 



1 "Bedeutung der Darmbakterien fur die Ernahrung," Archiv 

 /. Hyg., xlii, p. 48, 1902. 



2 "Note sur I'influence des microbes dans le development des 

 tetards," Ann. de I'Inst. Past., xv, p. 631, 1901. 



3 " Morphologische und biologische Untersuchungen iiber die 

 Darmbakterien des Sauglings," IV. "Der Schottelius Versuch 

 am Kaltbltiter," Jahrb. /. Kinderheilk., xii, p. 467, 1905. 



