102 THE HORSE IN HEALTH AND DISEASE 



The function of the kidneys is, concisely, to elaborate the urine. 

 Careful study has shown that in doing this they are active in main- 

 taining (1) the concentration of the blood by regulating the salt 

 content; (2) the volume of the blood by regulating the water con- 

 tent; (3) the neutral reaction of the blood by converting sodium 

 acid phosphate to sodium phosphate. Furthermore, when the 

 Hver fails to function properly the kidneys compensate by eliminat- 

 ing larger amounts of ammonia and other waste products than they 

 do normally. 



Urine is the most important excretion of the body. By it are 

 eliminated the nitrogenous products of metabolism, also the water 

 and soluble mineral substances. The amount and composition 

 varies with the age, the character of the food and drink, and the 

 state of metabolism. The average amount voided in twenty-four 

 hours is about 3000 to 4000 c.c, but may be as much as 9000 c.c. 

 When sweat is profusely excreted the urine is proportionately 

 reduced in amount. It is alkaline in reaction unless the animal 

 is starved. Equine urine has a specific gravity of about 1035, and 

 is turbid from the presence of the carbonates of lime which it con- 

 tains. The most important organic constituents are : urea, ammo- 

 nium salts, diureids, creatinin, and carbonic, uric, and hippuric 

 acids. Of these, urea and hippuric acid are found in relatively 

 large quantities. The former comes from the putrefaction of 

 proteins in the intestines, while the latter is formed chiefly from 

 the benzoic acid in the roughage, and is present in larger amounts 

 upon a diet consisting mostly of hay or grass than when concen- 

 trates are fed. 



THE REPRODUCTIVE ORGANS OF THE STALLION 



Starting with the testicles as the central structures of the 

 male genital tract, the following organs are found in succession — 

 the testicles and their covering, the scrotum, the vas deferens, the 

 seminal vesicles, the prostate and Cowper's glands, and the penis 

 (Fig. 32). 



The testicles are two egg-shaped glands situated in the inguinal 

 region. They are composed of glandular tissue and have a worm- 

 like appendage of seminiferous tubules known as the epididymis. 

 They are developed in the sublumbar region, and may descend 

 prior to birth through the inguinal canal into the scrotum. In the 

 majority of cases the colt is several weeks old before they can be 



