THE URINE. 



395 



that no precipitate is formed on the addition of sodium hyposul- 

 phite, but upon the large amount of acid salts, particularly acid 

 sodium phosphate, which it invariably contains. A strictly veg- 

 etable diet renders man's urine alkaline, and it is said to become 

 less acid after meals. In the herbivorous mammalia the urine is 

 normally alkaline so long as their digestion is going on, but when 



FIG. 175. 



Diagram showing the relation borne by the blood vessels to the tubules of the kidney. 

 Tue upper half corresponds to the cortical, the lower to the medullary part of the organ. 

 The plain tubes are shown separately on the ri^ht, and the vessels on the left. The 

 darkly shaded arteries send off straight branches to the pyramid and larger interlobular 

 branches to the glomeruli, the efferent vessels of which form the plexus around the con- 

 voluted tubes. 



they are deprived of food for some time it becomes acid, showing 

 that the alkalinity depends upon their diet. 



The specific gravity of urine varies greatly at different times, 

 commonly, however, ranging between the figures 1015-1020. 

 After copious drinking it may go as low as 1003, and after pro- 



