410 EXCRETION. 



dominal muscles and diaphragm, are very slight, and the flow of urine along the urethra 

 is aided by the contractions of its muscular walls and the action of some of the perineal 

 muscles, the most efficient being the accelerator urinaB ; but with all this muscular action 

 a few drops of urine generally remain in the male urethra after the act of urination is 

 accomplished. The process of evacuation of urine in the female is essentially the same 

 as in the male, with the exception of the slight modifications due to differences in the di- 

 rection and length of the urethra. 



The movements of the bladder are under the control of the nervous system. Accord- 

 ing to the researches of Budge, the influence of the nervous system operates through the 

 sympathetic, and he has described a centre in the spinal cord, which presides over the con- 

 tractions of the lower part of the intestinal canal, the bladder, and the vasa deferentia. 

 This he calls the genito-spinal centre, and he has located it, in experiments upon rabbits, 

 in the spinal cord, at a point opposite the fourth lumbar vertebra. From this centre, the 

 nervous filaments pass through the sympathetic nerve communicating with the ganglion 

 which corresponds to the fifth lumbar vertebra. 



Properties and Composition of the Urine. 



The importance of an exact knowledge of the properties and composition of the urine 

 has long been recognized by physiologists ; and our literature is full of observations, more 

 or less valuable, upon this subject, dating from the discovery of urea, by Hillaire Rouelle, 

 in the latter part of the last century, to the present time. It is impossible, however, to 

 follow out in detail even the most important of the chemical researches upon the differ- 

 ent urinary constituents, without exceeding the limits of pure human physiology ; and 

 the observations of the earlier authors have now little more than an historical interest. 

 But this can hardly be said of the analysis of the urine by Berzelins, made early in the 

 present century; for, even in recent authoritative works upon physiology, these are 

 quoted as the most elaborate and reliable of the quantitative examinations of the renal 

 excretion. In treating of this subject, we propose to give simply the chemistry of the 

 urine as it is understood at the present day, dwelling particularly upon its relations to the 

 physiology of nutrition and disassimilation. In doing this it will be necessary to con- 

 sider carefully the quantity, specific gravity, reaction, etc., of the urine, with the varia- 

 tions observed under different physiological conditions. 



General Physical Properties of the Urine. The color of the urine is very variable 

 within the limits of health, and it depends to a considerable extent upon the character of 

 the food, the quantity of drink, and the activity of the skin. As a rule, the color is yel- 

 lowish or amber, with more or less of a reddish tint. The fluid is perfectly transparent, 

 free from viscidity, and exhales, when first passed, a peculiar, aromatic odor, which is by 

 no means disagreeable. Soon after the urine cools, it loses this peculiar odor and has the 

 odor known as urinous. This odor remains until the liquid begins to undergo decomposi- 

 tion. The color and odor of the urine are usually modified by the same physiological 

 conditions. When the fluid contains a relatively large amount of solid matters, the color 

 is more intense and the urinous odor is more penetrating ; and, when its quantity is 

 increased by an excess of water, the specific gravity is low, the color pale, and the odor 

 faint. The urine passed in the morning is usually more intense in color than that passed 

 during the day. 



It is somewhat difficult to measure the exact temperature of the urine at the moment 

 of its emission. In the observations on this subject, by Dr. Byasson, in which a very 

 delicate thermometer was used and extraordinary care was taken to prevent any change 

 in temperature before the estimate was made, the temperature, under physiological con- 

 ditions, varied but a small fraction of a degree from 100 Fahr. It is important to know 

 the normal temperature of the urine, as it is liable to vary very considerably in certain 



