!&.TJ6UST 13, 1915] 



SCIENCE 



211 



nary conditions appears to diminish, al- 

 though there are even in the feeal eon- 

 tents great numbers of living organisms. 



The significance of the intestinal flora 

 has been variously interpreted. Various 

 theories have been proposed to explain 

 their relation to the well-being of man. 

 The theory which has received the greatest 

 attention is that one which assumes that 

 the normal intestinal bacteria assist the 

 digestion of food for the host through the 

 elaboration of certain ferments, and also 

 that these organisms are under normal con- 

 ditions in a sense a protection to the host in 

 that their activities are in opposition to 

 those of adventitious pathogenic bacteria, 

 which might otherwise gain a foothold in 

 the intestinal tract and become invasive. 

 A certain amount of theoretical evidence 

 was originally brought forth in support of 

 the digestive action of the intestinal bac- 

 teria : it was assumed that in the herbivora 

 certain cellulose-dissolving bacteria were 

 very active and that the activities of these 

 bacteria made assimilable the otherwise re- 

 sistant cellulose. 



Certain observers have attempted to ap- 

 proach the problem of the significance of 

 the intestinal bacteria from another point 

 of view. Nuttall and Thierfelder de- 

 livered guinea-pigs by Cesarean section 

 and attempted to raise them in a sterile en- 

 vironment on sterile food. For two weeks 

 these sterile guinea-pigs increased in 

 weight and appeared to be reasonably 

 healthy. These observers drew the conclu- 

 sion that the intestinal bacteria were not 

 necessary for the well-being of these guinea- 

 pigs at least. These experiments were not 

 accepted by Schottelius as being aonclusive. 

 He claimed that the experiments were not 

 carried on long enough. Schottelius ex- 

 perimented with chicks hatched from 

 sterile eggs. Parenthetically, it should be 

 remarked that Schottelius had the greatest 



difficulty in finding sterile eggs to start 

 with. However, after considerable investi- 

 gation he succeeded in getting a consider- 

 able number of sterile eggs which he di- 

 vided into three groups. These were in- 

 cubated under sterile conditions, and the 

 chicks developing from one group were 

 kept in an absolutely sterile environment 

 and fed on sterile food; a second group 

 were kept under the same conditions for 

 ten days and then fed with infected food; 

 the third group were controls and were 

 kept under ordinary conditions. The first 

 group, the sterile chicks, did well for ten 

 days, but after that time their development 

 was seriously retarded. The second group 

 also did weU for ten days, and then, as the 

 first group began to exhibit signs of ab- 

 normalities, they were placed on infeeted 

 food: they gained rapidly. The third 

 group, kept under ordinary conditions, did 

 well from the start. Schottelius believed 

 that his experiments showed that the in- 

 testinal bacteria were necessary for the de- 

 velopment and well-being of chicks. 



Madame Metschnikoff made similar ob- 

 servations on tadpoles, and Moro per- 

 formed the same experiments with turtles. 

 These observers agree with Schottelius that 

 the intestinal flora appear to be necessary 

 for the well-being of the animals they ex- 

 perimented on. 



A line of evidence which is somewhat 

 different from this was brought forward by 

 Levin. He examined the fecal contents of 

 many Arctic mammals in the Arctic re- 

 gions, and he found few or no bacteria in 

 them. He believed that an intestinal flora 

 was unnecessary for the development of 

 these animals. It should be remarked par- 

 enthetically, however, that Arctic mammals 

 brought to the temperate regions rapidly 

 acquire an intestinal bacterial flora, and 

 these organisms do not seem to interfere 

 with the well-being of their host. 



