DRUGS ACTING ON THE URINARY ORGANS 55 



behind. In the case of the herbivora the urine is alkaline, 

 because there are larger quantities of magnesium and 

 calcium salts in the food, which precipitate phosphoric acid 

 in the stomach, and because there is an excess of alkaline 

 sodium and potassium salts in the blood. The urine may 

 best be made acid by benzoic acid, which is converted into 

 hippuric acid during its passage through the kidneys. 

 Salicylic acid, the mineral acids (except nitric acid), and 

 large quantities of the vegetable acids tend to acidify the 

 urine in a less degree. An acid urine may be made alkaline 

 by alkalies, as salts of potassium, lithium, sodium and 

 calcium, together with the vegetable salts, tartrates, citrates 

 and acetates, which circulate as carbonates in the blood. 

 Drugs promoting diuresis make the urine less acid because 

 the basic sodium phosphate in the blood is not* so readily 

 broken up in the kidney when it diffuses through the cells 

 in great dilution. Nitric acid renders the urine slightly 

 alkaline by being converted into and eliminated as ammonia, 

 while ammonia fails to make the urine alkaline because it is 

 transformed into urea, uric and nitric acids (?). 



Uses. — Benzoic acid is sometimes of benefit in acidifying 

 and disinfecting an alkaline decomposing urine of pyelitis 

 or cystitis.* The alkalies are thought to be useful in 

 alkalizing the blood in certain disorders (rheumatism, 

 haemoglobinsemia, etc.), and the urine of carnivora, to prevent 

 the precipitation of uric acid in the urine or to aid its solu- 

 tion when already precipitated. 



Drugs Influencing the Composition of Urine. 



Drugs contracting efferent vessels of the malpighian 

 bodies diminish the flow of blood and urea-excretion and 

 increase the elimination of water ; while those dilating the 

 afferent vessels cause more blood to pass through the kidney 

 and promote the secretion of solids and water. Drugs 

 stimulating the cells of the convoluted tabes augment 

 especially the urinary solids. The composition of the urine 



* Recently urotropin has been used more successfully for these purposes. 



