DIGESTION AND ABSORPTION IN THE INTESTINES. 719 



alkaline, and when carbohydrates are used the reaction may not only 

 be acid to phenolphthalein, but also to the stronger indicators. On 

 the whole, therefore, it would seem probable that the small amount 

 or total lack of proteid putrefaction in the small intestine is due in 

 part to the rapid absorption of the digested proteid 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 proteids. When the former 

 have conditions favorable for growth, their increase in some way 

 affects injuriously the proteid bacteria.* 



Bacterial Action in the Large Intestine. In the large intestine 

 proteid putrefaction is a constant and normal occurrence. The 

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

 escaped digestion and absorption is in turn acted upon by the bacteria 

 and undergoes so-called putrefactive fermentation. The splitting 

 up of the proteid 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 amido-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 OS0 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 NOS0 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 proteid 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 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. 



