" INFECTIONS OF THE DIGESTIVE TRACT 



bacterial inhabitants numerous but they represent 

 many species and varieties. 



The knowledge that the digestive tract is so rich in 

 bacterial forms of life has led many physiologists to 

 inquire into the biological meaning of this remarkable 

 fact. Pasteur expressed a belief that these bacterial 

 inhabitants are essential in some way to the life of the 

 individual which harbors them. Nut tall and Thier- 

 f elder, 1 in their well-known experiments, attempted to 

 rear guinea-pigs delivered by Csesarian section and fed 

 on quite sterile food. As the animals lived and increased 

 in weight, the experimenters concluded that the intestinal 

 bacteria are not essential to normal nutrition. This 

 view, as will be presently seen, gets support from the 

 observations of Levin 2 , that some animals of the Arctic 

 region, as polar bears, have no bacteria in the digestive 



appears, however, that this is an under-estimate of the living bac- 

 teria. It may possibly hold true of the aerobic bacteria which 

 will grow on ordinary media. But we know that there are often 

 many aerobes and anaerobes in the intestine which do not grow on 

 ordinary media. In some instances there are very many strict 

 anaerobes (e.g. B. aerogenes capsulatus) which appear only on 

 specially prepared media on anaerobic plates. These, of course, 

 do not come into any count made in ordinary ways. Even the 

 numbers of living colon bacilli are subject to great variations. In 

 the same individual there may be at one tune a considerable pro- 

 portion of cultivable (living) bacilli. In a state of constipation the 

 number of cultivable colon bacilli may become very small. This 

 death of bacteria in the lower bowel during constipation doubtless 

 depends mainly on a failure of food supply and absence of moisture. 



1 " Thierisches Leben ohne Bakterien im Verdauungskanal," 

 Zeitschr. f. physiol Chem., xxi, p. 109, 1895; xxii, p. 62, 1896; 

 xxiii, p. 231, 1897. 



2 " Bakteriologische Darmuntersuchungen," Skandinavisches 

 Archiv /. Physiol., xvi, p. 249, 1904. 



