THE LARGE INTESTINE 403 



mucus, and little or no oxygen is present. The conditions thus 

 favour the growth of anaerobic organisms, and their action consists 

 of oxidations and reductions, rather than of hydrolytic changes, 

 such as are occasioned by enzymes. Proteins and carbohydrates 

 are chiefly acted upon, fats but little. The action upon carbohydrates 

 is often referred to as fermentation, that upon proteins as putre- 

 faction. The same bacteria do not act upon both kinds of food- 

 stuffs; indeed, they are antagonistic to each other to a certain 

 extent. The protein-decomposing bacteria are of many kinds, the 

 chief of which is Bacillus putrificus. They are anaerobes, working 

 in the absence of oxygen. The bacteria which act upon carbohydrates, 

 on the other hand, are aerobes, the chief being B. coli and B. lactis 

 aerogenes. 



Protein decomposition leads to the formation of such bodies as 

 sulphuretted hydrogen, methyl-mercaptan, marsh gas, ammonia, 

 carbon dioxide, lower fatty acids, phenyl-acetic and phenyl-propionic 

 acids, phenol, cresol, indol, skatol. The first-named bodies are generally 

 passed per rectum ; the last four bodies are absorbed* into the system, 

 and are harmful. If only absorbed in small amounts, they are arrested 

 in the liver, combined with sulphuric acid, and converted into the 

 ethereal sulphates which are excreted in the urine. If absorbed 

 in larger amounts, they escape this action of the liver, and there then 

 follows a general feeling of unfitness and depression, headache, and 

 various other nervous symptoms, due to alimentary toxaemia. 



Normally, there is no formation in the large gut of putrescin and 

 cadaverin, bodies which result from protein decomposition outside 

 the body. These are only found in special conditions, such as 

 dysentery and cystinuria. The difference between eiizymic and 

 bacterial action upon protein can be appreciated by placing in an incu- 

 bator at 37 C. two flasks containing minced meat in alkaline fluid. 

 The meat in one flask is acted upon by trypsin, bacterial action being 

 stopped by some toluol; the meat in the other is acted upon by any 

 bacteria which happen to be present. After two or three days, the 

 flask containing the enzymic digest has a peculiarly faint,, but not 

 repulsive, smell; the flask containing the products of bacterial action 

 stinks. 



Carbohydrate fermentation leads to the formation of carbon dioxide, 

 hydrogen, butyric, lactic, and acetic acids. The two processes proceed 

 simultaneously in different parts of the intestine. Generally speaking, 

 carbohydrate fermentation leads to the formation of a greater bulk 

 of gas of a less unpleasant nature than the smaller amount of gas 

 derived from protein decomposition. 



Under normal healthy conditions, protein decomposition does not 

 proceed to the same extent as outside the body. There is consider- 

 able discussion as to the reason of this. It has already been mentioned 

 that there is an antagonism between the different kinds of bacteria, 

 and the presence of carbohydrate may be partly responsible for this 

 limited action. Milk in the diet, and especially milk-sugar lactose 

 arc said to be particularly efficient in limiting the putrefaction of 



