808 PHYSIOLOGY OF DIGESTION AND SECRETION. 



sion as to the conditions that restrain the protein putrefaction in 

 the small intestine. It has been pointed out that some of the bac- 

 teria of the small intestine, Bacillus coli, for example, do not cause 

 protein hydrolysis as long as carbohydrate material (sugar) is 

 present,* so that the mere presence of carbohydrate material 

 serves to protect the protein from the action of the bacteria. 

 In addition, as long as carbohydrates are present and are under- 

 going fermentation, the organic acids produced tend to neutralize 

 the alkalinity of the intestinal secretion, and may even give an acid 

 reaction to the intestinal contents. An acid reaction is unfavor- 

 able to the activity of the bacteria that attack the proteins, and 

 in this way, under conditions of a normal diet, the process of putre- 

 faction in the small intestine is- warded off. From this standpoint 

 it would seem to follow that the nature of the bacterial activity 

 in the small intestine will vary with the character of the diet and, 

 moreover, that the diet may be chosen intentionally so as to 

 favor one or the other kind of bacterial action. 



Bacterial Action in the Large Intestine. In the large intestine 

 protein putrefaction is a constant and normal occurrence. The 

 reaction here is stated to be alkaline, and whatever protein may have 

 escaped digestion and absorption is in turn acted upon by the bac- 

 teria and undergoes so-called putrefactive fermentation. The split- 

 ting up of the protein molecule by this process is very complete, and 

 differs in some of its products from the results of hydrolytic cleavage 

 as caused by acids or by trypsin. The list of end-products of putre- 

 faction is a long one. Besides peptones, proteoses, ammonia, and 

 the various ammo-acids, there may be produced such substances as 

 indol, skatol, phenol, phenylpropionic and phenylacetic acids, fatty 

 acids, carbon dioxid, hydrogen, marsh gas, hydrogen sulphid, etc. 

 Many of these products are given off in the feces, while others are 

 absorbed in part and excreted subsequently in the urine. In this 

 latter connection especial interest attaches to the phenol, indol, and 

 skatol. Phenol or carbolic acid, C 6 H 5 OH, after absorption is com- 

 bined with sulphuric acid, to form an ethereal sulphate (conjugated 

 sulphate) or phenolsulphonic acid, C 6 H 5 OSO 2 OH, and in this form 

 is found in the urine. So also with cresol. The indol, C 8 H 7 N, and 

 skatol (methyl-indol), C 9 H 9 N, are also absorbed, undergo oxidation to 

 indoxyl and skatoxyl, and are then combined or conjugated with 

 sulphuric acid, like the phenol, and in this form are found in the urine 

 C 8 H 6 NOSO 2 OH, or indoxyl-sulphuric acid, and C 9 H 8 NOSO 2 OH, 

 skatoxyl-sulphurie acid. These bodies have long been known to 

 occur in the urine, and the proof that they arise primarily from putre- 

 faction of protein material in the large intestine is so conclusive as 



* See Kendall, "Boston Med. and Surgical Journal," 1910, 163, 322, and 

 "Wisconsin Med. Journal," June, 1913. 



