224 PHYSIOLOGY CHAP. 



the intestinal bacteria almost exclusively of the species Bacterium 

 coli and its varieties, to which the Bacillus mesentericus (which 

 resembles that of typhoid) is frequently added. It is true that 

 not a few authors (Macfadyeu, Nencki and Sieber, Gessner, 

 Ciechowsky and Jaworsky), have described 7 species in the human 

 intestine under normal conditions, and Vignal 10 distinct species, 

 4 of which live in the mouth as well ; but in all probability many 

 of these bacteria must be regarded not as permanent but merely 

 as casual inhabitants of the intestine. Innumerable researches 

 of many workers in hygiene and pathology (Maggiora, Jensen, 

 MacWeeney, Laveran, Celli, and others) on the faeces not merely 

 of normal individuals, but also of persons affected with dysentery 

 and cholera nostras, have yielded only pure or almost pure cultures 

 of Bacterium coli and its varieties. 



Bacterium coli under the microscope appears as a bacillus, 1-5 /A 

 long, 0*3-0 - 5 jj, broad. In gelatin cultures the colony assumes the 

 form of a small, round, greyish-white protuberance. On studying 

 its metabolism in vitro, it has been found to produce partial 

 alcoholic fermentation of glucose, lactic fermentation of lactose, 

 and direct cleavage of amygdalin into benzoic aldehyde and 

 hydrocyanic acid, with consumption of glucose. It does not 

 liquefy gelatin : it has the property of slowly coagulating milk 

 (in 4-5 days) and of slowly digesting fibrin, but not coagulated 

 egg-white ; lastly it gives off a strong and disagreeable smell of 

 putrefaction to the culture medium. It is, however, very probable 

 (infra) that under the special conditions of temperature and 

 environment in which their activity is manifested in the intestine, 

 these bacteria are capable of a more varied and energetic meta- 

 bolism, which is normally not pernicious, but may even be useful, 

 if not indispensable, to their host. 



The cause of this relative constancy of the intestinal bacteria, 

 notwithstanding that the most varied species of microbes continually 

 penetrate into the digestive tube, presents an. interesting problem. 

 That Blastomycetes and Sarcinae alone can live normally in 

 the stomach is readily explained by the acidity of the medium ; 

 but why Bacterium coli and its allied species or varieties alone take 

 up their permanent abode in the intestine, is not easy to explain 

 (as Fermi noted) by the reaction of the environment, since this 

 should be suitable for the development of the most varied species 

 of microbes. 



It is a fact that Bacterium coli is far less plentiful in the 

 air, in. water, and in the soil than many other microbes, which 

 must therefore penetrate in much larger numbers into the digestive 

 canal (Schardinger). It is a fact that it is not the most resistant 

 to the action of the gastric juice, and that, on the other hand, 

 many microbes penetrate per anum, and are therefore not exposed 

 to the sterilising action of the gastric juice (Escherich, W. Schild). 



