DIGESTION 221 



and fourth portion of the double colon, with their pea-soup-like 

 contents, on the surface of which gas bubbles are constantly 

 breaking. It may well be that these two places are the active 

 seats of the final transformation of cellulose, the caecum dealing 

 with that which has already been acted upon in the stomach and 

 small intestines, and the fourth colon being concerned with the 

 more refractory cellulose, which has required prolonged macera- 

 tion in the large intestines before becoming capable of solution. 

 This is rather supported by the remarkably rapid change in the 

 character of the contents in the single colon, the pea-soup-like 

 condition giving way, in the space of a few inches, to the 

 appearance presented by ordinary normal faeces. 



The large intestines cannot exist entirely for the solution of 

 cellulose. There are other processes going on, chief of which is 

 the bacterial attack on the unabsorbed protein products of the 

 small intestines. The small intestine may be regarded as free 

 from putrefactive processes ; in fact, it is only towards the ileum 

 that the unpleasant products of pancreatic digestion can be 

 detected. In the large intestine, on the other hand, putrefactive 

 processes are evident throughout ; the bacteria are here engaged, 

 among other things, in attacking the unabsorbed products of 

 protein digestion, and reducing them to simpler end-products, 

 such as proteoses, peptones, amido-acids, indol, skatol, phenol, 

 phenyl-propionic, phenyl-acetic and fatty acids, with the 

 evolution of C0 2 , H 2 , H 2 S, and CH 4 . These end-products are 

 got rid of either through the faeces, or they are absorbed into the 

 blood, taken to the kidneys, and, combining with sulphuric acid, 

 are got rid of through the urine ; especially is this the case with 

 phenol, indol, and skatol. 



Metschnikoff has made a special study of the organisms living 

 in the intestinal canal of man, and has arrived at the conclusion 

 that in the myriad population of the intestinal tract there are 

 at least three anaerobic organisms which can produce very viru- 

 lent poisons. These poisons, which are of the aromatic series, 

 phenols and indols, are absorbed by the intestinal wall. Metschni- 

 koff regards the colon with grave suspicion, and believes that 

 it is the cause of men not dying from old age. It certainly 

 cuts short the useful life of many horses. 



As the material moves towards the rectum it becomes drier 

 and drier, and more thoroughly formed into balls by the action 

 of the bowel-sacs, which squeeze the mass into a round or oval 

 shape. The contents of this portion are still alkaline, or slightly 

 so. As we approach the anus a distinctly acid reaction is 

 obtained on the surface of the faeces, though at this time the 

 interior of the ball may be, and often is, alkaline ; the converse of 

 this may also be observed. In the rectum the single balls collect 



