80 HUMAN PHYSIOLOGY. 



trading the muscle and expelling the urine. If the act is to be sup- 

 pressed, voluntary impulses inhibit the detrtisor centre and possibly stimu- 

 late the sphincter centre. * 



The genito- spinal centre controlling these movements is situated in that 

 portion of th'e spinal cord corresponding to the origin of the 3d, 4th and 

 5th sacral nerves. 



URINE. 



Normal Urine is of a pale yellow or amber color, perfectly transparent, 

 with an aromatic odor, an acid reaction, a specific gravity of 1.020, and a 

 temperature when first discharged of 100 Fahr. 



The color varies considerably in health, from a pale yellow to a brown 

 hue, due to the presence of the coloring matter, urobilin or urochrome. 



The transparency is diminished by the presence of mucus, the calcium 

 and magnesium phosphates and the mixed urates. 



The reaction of the urine is acid, owing to the presence of acid phos- 

 phate of sodium. The degree of acidity, however, varies at different 

 periods of the day. Urine passed in the morning is strongly acid, while 

 that passed during and after digestion, especially if the food is largely vege- 

 table in character, is either neutral or alkaline. 

 The specific gravity varies from 1.015 to 1.025. 



The quantity of urine excreted in 24 hours is between 40 and 50 fluid 

 ounces, but ranges above and below this standard. 



The odor is characteristic, and caused by the presence of taurylic and phe- 

 nylic acids, but is influenced by vegetable foods and other substances elimi- 

 nated by the kidneys. 



COMPOSITION OF URINE. 

 Water, ..................... 967. 



Urea, ...................... 14-230 



Other nitrogenized crystalline bodies, uric acid, prin- 



cipally in the form of alkaline urates. 

 Creatin, creatinin, xanthin, hypoxanthin. 

 Hippuric acid, leucin, tyrosin, taurin, cystin, all in f 



small amounts, and not constant. 

 Mucus and pigment. 

 Salts : 

 / Inorganic, principally sodium and potassium sul- "] 



phates, phosphates and chlorides, with magnesium 

 I and calcium phosphates, traces of silicates and K 



V chlorides. 



\Organic : lactates, hippurates, acetates, formates, 

 i whiclTappear only occasionally. 

 Sugar, ................... ..a trace. 



Gases (nitrogen and carbonic acid principally). 



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