164 MANUAL OF BACTERIOLOGY. 



Bacteria are always present to a greater or less extent in the 

 stomach and intestines except for a few hours after birth. 

 The alimentary tract of new-born infants and the meconium 

 are sterile. In from four to eighteen hours organisms begin to 

 appear. They may enter either from the mouth or the anus. 

 There seems to be no constancy in the nature of the forms 

 which are found at first, but their character depends upon the 

 surroundings. 



The species of bacteria found in the stomach are less con- 

 stant than those of the intestines; and under normal circum- 

 stances they seem to be those introduced from the mouth. 

 Different investigators, at all events, have met with quite 

 different species in the stomach. It appears that the hydro- 

 chloric acid (about 2 parts per thousand) present in the gastric 

 juice at the height of digestion possesses decided germicidal 

 properties. This germicidal power exercises a restraining in- 

 fluence upon fermentation due to bacteria, and probably serves 

 as a safeguard against the introduction of pathogenic germs 

 into the intestines. That is particularly important in the case 

 of the spirillum of cholera, which is excessively sensitive to the 

 action of acids. Nevertheless, many bacteria are able to reach 

 the intestines uninjured, as the acidity of the gastric juice does 

 not reach its height until some hours after eating. Such 

 bacteria will be those which are most resistant and those which 

 form spores. In the intervals when hydrochloric acid is ab- 

 sent from the stomach, lactic acid appears. It is formed from 

 carbohydrates by a large number of species of bacteria. In 

 conditions of fermentation, sacrina ventriculi and yeasts may 

 be present in large numbers; in the healthy stomach they occur 

 in much smaller numbers. 



The intestine of the infant in whom feeding has become 

 well established was found by.Escherich to contain two prin- 

 cipal species of bacteria in the lower part of the intestine the 

 bacillus coli communis, in the upper part the bacilus lactis ; 



