144 MANUAL OF BACTERIOLOGY. 



mentation 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 absent from the 

 stomach, lactic acid appears. It is formed from carbohydrates 

 by a large number of species of bacteria. In conditions of 

 fermentation, sarcina 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 principal 

 species of bacteria — in the lower part of the intestine the bacillus 

 coli communis, in the upper part the bacillus lactis aerogenes. 

 More recently it has been shown that the stools of milk-fed 

 infants, and to a less extent of adults, contain large numbers of 

 anaerobic bacilli, which stain by Gram's method (bacillus 

 bifidus — Tissier, bacillus acidophilus — Moro). These bacteria 

 have not been fully studied.* 



The number of bacteria in a milligram of human fecal 

 matter has been estimated at from seventy thousand to thirty- 

 three million. It is estimated that about one-third of the fecal 

 matter of adults consists of bacteria. The small intestine of 

 adults has been found by different observers to contain very 

 different species. f The majority of these appear to have been 

 introduced from the mouth in food or water. The bacillus 



* Metchnikoff. Les Microbes Intestinaux. Bulletin de I'lnslilui Pasteur. 

 May IS and 30, 1903. 



t Ford. Classification of Intestinal Bacteria, etc. Studies from the Royal 

 Victoria, Montreal. March, 1903. 



