100 PRINCIPLES OF PHYSIOLOGY 



digested, and for various substances excreted 

 by numerous tubular glands. The secretions 

 of the great bowel do not take an active part 

 in true digestion. Putrefactive processes also 

 are carried on, even in the small bowel, and 

 still more in the larger bowel, and these 

 processes, due to the activities of numerous 

 bacteria, still further split up the protein 

 molecules, with the production of offensive 

 smelling bodies, indol, skatol, phenol, etc. 

 These bodies, by uniting with sulphuric 

 acid arising from sulphates (originating from 

 the sulphur of proteins), form etherial sul- 

 phates, such as indoxyl-sulphate of potassium. 

 This body is called indican, and is voided 

 in the urine. Such fermentative and putrefac- 

 tive processes, all due to specific organisms, 

 also attack carbo-hydrates and fats, producing 

 lactic acid, butyric acid, sulphuretted hydro- 

 gen, carbonic acid, and other substances. 

 The absorption of these may cause a kind of 

 auto-poisoning of the individual. 



53. It will be seen that all the constituents 

 of food are now soluble and ready for absorp- 

 tion, This is accomplished mainly in the 



