718 PHYSIOLOGY OF DIGESTION AND SECRETION. 



normal feces, provided care was taken with the diet. An excess of 

 fat or indigestible material caused diarrhea and serious loss of food 

 material in the feces. An interesting feature in the large intestine 

 is the marked absorption of water. In the small intestine no doubt 

 water is absorbed in large quantities, but its loss is evidently made 

 good by osmosis or secretion of water into the intestine, since the 

 contents at the ileocecal valve are quite as fluid as at the pylorus. 

 In the large intestine the absorption of water is not compensated by 

 a secretion; the material becomes more and more solid as it ap- 

 proaches the rectum, and is thus formed into the feces. The alkaline 

 reaction of the contents of the large intestine makes a favorable 

 environment for the growth of bacteria, particularly the putrefactive 

 bacteria that attack proteid material. Putrefaction is a normal 

 occurrence in the large intestine, and much interest has been shown 

 in its extent and its possible physiological significance. 



Bacterial Action in the Small Intestine. Bacteria are con- 

 stantly present in both the large and the small intestine. Under 

 normal conditions, however, it would seem that in the small intestine 

 only those bacteria capable of fermenting carbohydrate food show any 

 distinct activity. Putrefactive fermentation of proteid material 

 is limited or absent in this part of the intestine as long as the products 

 of proteid digestion are promptly absorbed. Conditions that prevent 

 or retard this absorption favor the occurrence of proteid putrefaction. 

 Opinions among investigators differ as to the means by which the 

 proteid contents are protected from the action of the bacteria. It 

 has been shown that the presence of carbohydrate material has a 

 restraining effect upon proteid putrefaction. The simplest explana- 

 tion of this relation is that the fermentation of the carbohydrates 

 gives rise to a number of organic acids, lactic, acetic, etc., and 

 these acids inhibit the action of the proteid bacteria. To make this 

 explanation satisfactory, however, it is necessary to show that the 

 contents of the small intestine possess an acid reaction. Concerning 

 this point, however, opinions also differ. The secretions of the small 

 intestine are all alkaline and we should expect their contents to have 

 this reaction. Examination shows that the contents of the small 

 intestine are acid or not according to the indicator used. With 

 phenolphthalein they may give an acid reaction, while with litmus, 

 lakmoid, etc., no such reaction is obtained.* Such a result as this 

 indicates that no strong organic acids, such as acetic and lactic, 

 are present, the phenolphthalein being affected possibly by the C0 2 . 

 As Munk has stated, however, it seems that the contents of the small 

 intestine throughout the duodenum and jejunum are at least never 



* Consult Macfadyen, Nencki, and Sieber, loc. cit.; Moore and Bergin, 

 "American Journal of Physiology," 3, 316, 1900; Munk, " Centralblatt f. 

 Physiologie," 16, 33 and 146, 1902. 



