128 PHYSIOLOGY. 



throughout the entire alimentary canal from mouth to anus, but are 

 more numerous in the intestines, particularly in the large one, where 

 their action is very marked upon matters i caching it, so as to give 

 rise to the term "bacterial digestion/' In the stomach, under nor- 

 mal conditions, the putrefactive activity of the bacteria is neutralized 

 and the germs themselves are killed by the free hydrochloric acid of 

 the gastric juice. It is in the intestines, where the secretions are 

 alkaline, that the best media are found for their culture and develop- 

 ment. 



It has been suggested that bacterial digestion was necessary to 

 the economy, because it accomplishes so many things. But it has 

 been shown by Nuttal that, by removing guinea-pig foetuses directly 

 by incision from the uterus, and with antiseptic care, and then 

 keeping them in "a sterile chamber, receiving sterilized air and fed 

 on sterile milk, they grew. When their intestinal contents were 

 examined no bacteria were found. Hence the inference is that 

 bacteria are not necessary for good digestion. 



The two chief bacteria are the lactic acid bacillus and the colon 

 bacillus. The former is found in the stomach at times and the 

 upper part of the small intestine. The colon bacillus chiefly lives 

 in the colon. These bacteria are aerobic; that is, they consume 

 oxygen in the action. Hence they are powerful reducing agents. 

 Thus they take oxygen from bilirubin and form stercobilin. But, 

 although these microbes use oxygen, they can also live without it. 

 On proteids the bacteria produce by their action proteoses and pep- 

 tones, and from tyrosin the aromatic bodies: phenol and cresol. 

 Indol and skatol are derived from tryptophane. On carbohydrates 

 the bacteria act like ptyalin and amylopsin; on fats they act like 

 steapsin, breaking up lecithin into cholin. Bacteria in the stomach 

 and intestine can set up five kinds of fermentation: (1) alcoholic; 

 (2) acetic; (3) lactic; (4) butyric; and (5) a form of fermentation 

 discovered by Drs. Herter and Baldwin the oxajic acid variety. 

 These fermentations may give rise to acute and chronic gastro-en- 

 teritis. In the intestine the fermentations will give rise to excessive 

 distension, diarrhoea, colic, and a loss of weight and strength. The 

 remote effects of these fermentations will be an increase of uric and 

 oxalic acid in the urine and of the acidity of the urine itself, causing 

 frequent urinations, especially at night. The best indication of 

 intestinal putrefaction is the aromatic or ethereal sulphates which 

 appear in the urine. The easiest test to detect the indoxyl sulphate 



