160 PHYSIOLOGICAL CHEMISTRY 



bladder before the urine is voided. Various gases may be pro- 

 duced, the condition being known as pneumaturia. 



If injected into the blood stream, urine has a toxic effect. This 

 is due in part perhaps to certain alkaloidal substances present 

 in small amounts, but also to disturbances in osmotic equilib- 

 rium. 



Spectroscopic examination of the urine is sometimes valuable 

 in the detection of blood or bile pigments. 



Reaction. The urine of a normal healthy individual may 

 vary considerably in chemical reaction, thus it may be acid, 

 neutral or alkaline. The reaction depends primarily on the 

 nature of the diet. On a meat (protein) diet, the urine is acid, 

 on a vegetable (non-protein) diet the urine may be alkaline. 

 Thus the urine of carnivora is acid, that of herbivora alkaline. 

 If either class of animal is forced to eat the other class of 

 material, the reaction of the urine changes accordingly. In 

 starvation, the urine is acid, since an., animal thus becomes car- 

 nivorous, living upon its own tissues. At the beginning of gastric 

 digestion, the urine usually is alkaline, due to the abstraction 

 of available H-ions from the blood to form the gastric HC1. 

 Profuse sweating also may lower the acidity, since acid is carried 

 out through the skin. 



The effect of variations in diet upon the reaction of the urine 

 is due to the products formed in the breaking down of food 

 constituents. Proteins contain^ sulphur and phosphorus, which 

 are transformed into sulphuric and phosphoric acids, and 

 excreted largely in the form of acid salts and probably to a 

 slight extent as the free acids. These two factors are mainly 

 responsible for the acid reaction of urine, although there also 

 are small amounts of various organic acids. The organic acids 

 in vegetable products, on the other hand, are oxidized to C0 2 

 in the body, a portion of which is excreted in the urine as car- 

 bonate. The hydrolysis of these salts is responsible for an alka- 

 line reaction of urine. Ingesting organic acids such as citric, 

 malic, etc., which are burned to carbonates, actually increases 



