INTESTINAL MICRO-ORGANISMS 249 



gelatine is very rapidly liquefied. Bound yellow colonies 

 ■with bulging edges form on the gelatine plate, being larger 

 on the surface than in depth. In thrust-cultures the upper 

 part of the liquefied mass is coloured briek-red, and on 

 agar there develops a brick-red deposit with white edges. 

 Serum is liquefied, sometimes with, sometimes without, 

 pigmentation. On potato a brick-red deposit forms on the 

 jjlace of inoculation. Pigmentation depends upon the access 

 of air. This bacillus is distinguished from the Bacillus 

 prodigiosus, to which it has otherwise considerable resem- 

 blance, by its pathogenic action on animals, which it kills 

 with the symptoms of a severe gastro-enteritis. 



The Intestine 



Intestinal micro-organisms. — Passing from the stomach 

 along with the chyme, the micro-organisms reach the 

 internal surface of the intestine, an occurrence which, how- 

 ever, only becomes possible from the fact that certain of 

 them are capable of preserving their vitality notwithstanding 

 ihe gastric juice, or that the reaction and other qualities of 

 ihe juice itself are not such as to exert a prejudicial influence 

 on the microbes. The internal surface of the intestinal 

 mucous membrane contains very many micro-organisms, 

 and seems as a rule to afford a very favourable environment 

 for them, while the contents of the gut, whether liquid or 

 firm, show microbes in such abundance even under normal 

 conditions that of all parts of the body they are richest in 

 such organisms. 



The alkaline reaction of the intestinal secretion and the 

 length of time which food takes to pass through the intes- 

 tinal canal are important factors in favour of the growth of 

 micro-organisms. Duclaux ascribes to them a certain 

 amount of digestive significance, on the ground that their 

 activity is capable of assisting the physiological digestive 



