740 PHYSIOLOGY OF DIGESTION AND SECRETION. 



never alkaline, and when carbohydrates are used the reaction may 

 not only be acid to phenolphthalein but also to the stronger indica- 

 tors. On the whole, therefore, it would seem probable that the 

 small amount or total lack of protein putrefaction in the small intes- 

 tine is due in part to the rapid absorption of the digested protein 

 and in part to an unfavorable reaction. Some observers contend 

 that there is a struggle for existence or antagonism between the 

 bacteria acting upon carbohydrates and those living upon proteins. 

 When the former have conditions favorable for growth, their increase 

 in some way affects injuriously the protein bacteria.* 



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 amino-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 NOS0 2 OH, or indoxyl-sulphuric acid, and C 9 H 8 NOSO 2 OH, 

 skatoxyl-sulphuric 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 

 not to admit of any doubt. The amount to which they occur in 

 the urine is, therefore, an indication of the extent of the putrefaction 

 in the large intestine. 



Is the Putrefactive Process of Physiological Importance? 

 Recognizing that fermentation by means of bacteria is a normal 

 occurrence in the gastro-intestinal canal, the question has arisen 

 whether this process is in any way necessary to normal digestion and 

 nutrition. It is well known that excessive bacterial action may lead 

 * See Bienstock, " Archiv f. Hygiene," 39, 390, 1901. 



