DISTRIBUTION AND HABITAT OF THE BACTERIA. 725 



composition of the food as well as the course and stage of 

 digestion. The occurrence of an acid reaction in the 

 intestinal contents must cause marked alteration in the 

 bacterial life in the intestine. More especially do organic 

 acids, such as occur in the later decompositions of the 

 chyme, exert a particularly marked inhibitory action on 

 many bacteria ; it is only some forms which are excep- 

 tionally insensitive, such as lactic acid and butyric acid 

 bacilli, which still remain capable of development, and 

 thus gain the mastery the sooner. Anaerobes are also Anaerobes, 

 constantly found in the intestines, and often in such 

 large numbers that there can be no doubt that they 

 have multiplied there. This is easily intelligible, be- 

 cause in certain sections of the intestine, and in certain 

 layers of the intestinal contents, there is always a 

 deficiency of oxygen sufficient to permit the development 

 of anaerobes. 



Among the large numbers of intestinal bacteria the Pathogenic 

 saprophytes are most numerous, nevertheless those h^es^ne 

 bacteria which do not grow so quickly as the sapro- 

 phytes, and are hence as a rule hardly adapted for 

 concurrent growth with them, not uncommonly multiply 

 to a marked extent, and possibly grow in the folds of 

 the intestinal wall which are more removed from the 

 action of the saprophytes of the chyme. In this way 

 bacteria may develop in the intestine which are 

 dangerous to the body, partly by means of their 

 ptomaines, and partly by penetrating into the intestinal 

 wall and causing infection. 



We must await future investigations for a more 

 accurate knowledge of the intestinal bacteria, for an 

 isolation of the varieties which occur most frequently 

 or regularly, and also of those which only occur now and 

 then, and for facts as to their functions and their 

 effects.* This study is to some extent rendered difficult 

 by the fact, that in microscopical preparations made 



* While those sheets were passing* through the press, an extensive 

 research, which has just been published by TtScherich(Die Darmba&terien 

 des Sauglings, Stuttgart, 1886), forms an important beginning to the 

 investigations in this department. 



