PTOMAINES 143 



absorption of water, and the faecal residue stored until 

 ready for evacuation. The large intestine may be divided 

 physiologically into two parts : a -proximal part, consisting 

 of the ascending colon and the neighbouring half of the 

 transverse colon, whose function it is to provide a maximum 

 exposure of the contents to the intestinal wall, and a 

 distal part, consisting of the remainder of the colon, which 

 is concerned in the storage of faeces and in the process of 

 defsecation. From the nutritional point of view the 

 principal function of the large intestine is the absorption 

 of water. The glands of the intestinal wall give out a 

 mucous secretion, which has no enzymes. It serves to 

 lubricate the faeces. The chemical changes which occur 

 are due to bacteria, with which this part of the gut swarms. 

 Of these organisms the commonest is the Bacillus Coli. 



The organisms feed principally upon proteins, and in 

 particular upon certain products of protein hydrolysis — 

 tyrosin and tryptophane. From ty rosin they form carbohc 

 acid, from tryptophane scatol and indol, the substances 

 responsible for the characteristic odour of faeces. The 

 extent to which these compounds are formed depends 

 first upon the amount of proteolytic products reaching the 

 large intestine — that is to say, upon the efficiency of the 

 digestive processes; secondly, upon the degree of stasis 

 of the intestinal contents in this part of the gut. Phenol, 

 indol and scatol are hable to be absorbed, and when 

 absorbed are toxic. Normally, however, they are rendered 

 less toxic by combination with sulphuric acid and excretion 

 in the urine. 



Besides these substances, there are formed certain nitro- 

 genous bases usually known as " ptomaines." Of these 

 the commonest are histamine, cadaverine and putrescine. 

 They are formed by removal of CO2 from certain amino - 

 acids — the work, again, of bacteria. If absorbed into the 

 blood-stream they exert toxic effects. 



Intestinal bacteria also act upon carbohydrates, con- 

 verting them into lactic acid. 



