DIGESTION AND ABSORPTION IN THE INTESTINES. 815 



in the large intestine. We may assume that the indol and skatol 

 arise from the tryptophan group in the protein molecule, and the 

 phenol and cresol from the ty rosin and phenylalanin. There is 

 evidence that other more or less toxic substances belonging to the 

 group of amines are produced by the further action of the bacteria 

 on the amino-acids in the protein molecule. 



The general relation of the amines to the amino-acids may be expressed 

 by the formula 



RCH 2 CHNH 2 COOH CO, = RCH 2 CH 2 NH 2 . 



As a group they have a drug-like action on the body resembling that of 

 epinephrin that is, they may cause a rise of blood-pressure, acceleration 

 of heart, etc. Some of the amines that have been described are putrescin or 

 tetramethylendiamine from arginin, cadaverin or pentamethylendiamine from 

 lysin, imidazolethylamine from histidin, indolethylamine from tryptophan, 

 oxyphenylethylamine from tyrosin. 



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 to intestinal troubles, such as diarrhea, or to more serious inter- 

 ference with general nutrition owing to the formation of toxic prod- 

 ucts. It is, however, possible that some amount of bacterial action 

 may be necessary for completely normal digestion. As a special case 

 it has been pointed out that the gastro-intestinal tract is not pro- 

 vided with enzymes capable of acting upon cellulose, a material that 

 forms such an important constituent of vegetable foods. Bacteria, 

 on the other hand, may hydrolyze the cellulose and render it useful 

 in nutrition. Leaving aside this special case, the question as to the 

 necessity of bacterial action has been investigated directly by at- 

 tempting to rear young animals under perfectly sterile conditions. 

 Nuttall and Thierfelder* report some very interesting experiments 

 upon guinea-pigs in which the young animals from birth were kept 

 sterile and fed with perfectly sterile food. They found that the ani- 

 mals lived and increased in weight, and concluded, therefore, that the 

 intestinal bacteria are not necessary to normal nutrition. This con- 

 clusion is supported by the observations of Levin, f who finds that 

 animals in the Arctic regions in many cases have no bacteria in their 

 intestines. Schottelius t reports contrary results upon chickens. 



* Nuttall and Thierfelder, "Zeitschrift f. physiol. Chemie," 21, 109, 1895; 

 22, 62, 1896; 23, 231, 1897. 



t Levin, "Skandinavisches Archiv f. Physiologic," 16, 249, 1904. 

 t Schottelius, "Archiv f. Hygiene," 42, 48, 1902. 



