640 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



constituents. Uric and hippuric acids are the representatives of the 

 nitrogenous organic constituents. Uric acid and hippuric acid are found 

 in proportions which are governed by the character of the diet in the 

 same way as in the case of the horse. The mineral constituents are like- 

 wise dependent on the food, potassium and lime combinations bein°- 

 especially abundant. The urine of the ox is clear, yellowish, or greenish, 

 and possesses a peculiar, musky odor. Its specific gravity varies from 

 1020 to 1030, depending on the amount of water in the food. It is 

 always poorer in solids than the urine of the horse. It also contains less 

 sulphuric acid compounds, especially of the aromatic group, than horses' 

 urine. The phosphates are entirely absent, or present only in traces. 



The Urine of the Sheep and Goat is similar to that of the ox, but 

 shows great variation in the salts derived from the food. Its specific 

 gravity varies from 1006 to 1015 ; the amount from five hundred to eight 

 hundred and fifty cubic centimeters daily. Urea and hippuric acid are 

 present in the proportion of about two to three, the hippuric, contrary 

 to what is the case in the horse, being more abundant when on a diet of 

 young hay rich in proteids. 



The Urine of the Pig is clear, yellowish, with a faint alkaline reac- 

 tion ; specific gravity, 1010 to 1015. It contains urea, but rarely uric or 

 hippuric acids. The salts depend on the character of food. In general, 

 the urine resembles that of carnivora. 



The Urine of the Dog is deep yellow in color, acid reaction ; specific 

 gravity, 1050 when fed on meat. It is rich in urea, but contains but little 

 uric acid. Kreatin and indican are present, but no phenol. Mg salts are 

 in larger amount than Ca salts, while the chlorides are scanty ; sulphates 

 and phosphates abundant. It readily undergoes ammoniacal fermenta- 

 tions (from urea) and deposits phosphates. Its composition and character 

 likewise vary greatly with the nature of the food.* 



2. The Mechanism of Renal Secretion. — The substances which 

 exist in the urine in a state of solution also exist in the blood, and the 

 process of secretion of the urine is, therefore, largely a process of 

 mere infiltration. Nevertheless, certain constituents of the urine are 

 evidently manufactured in the kidney, since their presence has not yet 

 been detected in the blood. Renal secretion is thus possessed of two 

 factors,— a physical process of filtration and a process of true secretion 

 dependent upon the activity of the renal epithelium. 



The mechanism of the renal secretion is, to a certain extent, capable 

 of explanation by the study of the structure of the kidney. The kidney 

 is composed of a series of fine tubules, which, starting from the hilum 



* For further details as to the composition of the urine of the domestic animals under 

 different forms of diet the reader is referred to the " Encyelopsedie der Gesammten Thier- 

 heilkunde," Bd. iv, p. 202. 



