The Chemical Constituents of the Organism. 13 



benzoic acid, the union of which in the body produces 

 hippuric acid. For further remarks on this acid see the 

 chapter on the Urine. 



Bile Acids. — These probably originate from proteid de- 

 composition in the body, being furnished by glycocin and 

 taurin ; see Liver. 



Another group of nitrogenous bodies also connected with 

 proteid decomposition is characterized by the absence of 

 oxygen. Trimethylamine has been found in the blood of 

 the calf, and in urine. Indol and Skatol found in the faeces 

 are due to the decomposition of proteids produced by pan- 

 creatic digestion. These bodies are closely connected with 

 the indigo group, which, however, contains oxygen. 



Indigo occurs in the urine of herbivora ; it is derived 

 from indol, which by oxidation becomes indigo blue. In 

 the urine indican is found united with potassium sulphate, 

 and should skatol and indol pass by this channel they are 

 united with the same salt. 



The next great chemical group is the Non-nitrogenous. 

 Fat is composed of a mixture of glycerin and fatty acids . 

 the latter are known as olein, stearin, and palmitin, the 

 two latter form the solid fats ; olein and palmitin the more 

 liquid fats. In the sheep and ox the fat is very firm, and 

 stearin enters into its composition, whereas in the horse 

 the fat is more fluid, and olein and palmitin are the chief 

 components. 



The amount of fat in the body must depend upon the 

 feeding of the animal, and will obviously vary within 

 extreme limits ; in individual tissues marrow has the largest 

 amount — nerve, brain, milk, muscle, liver, bone, bile, and 

 blood, have proportions which decrease in the order 

 given. 



Special fatty acids are found in butter and milk. 

 The change which the fats undergo in the alimentary- 

 canal is discussed in the chapter on Digestion, whilst the 

 origin of fat in the body and its function is dealt with 

 under Nutrition. 



The Carbo-hydrates consist of several substances, which 



