COMPOSITION OF URINE. 357 



meal, and by several other accidental circumstances. The ex- 

 istence of these causes of difference in the composition of the 

 urine has led to the secretion being described under the three 

 heads of urina sanguinis, urina potus, and urina cibi. The 

 first of these names signifies the urine, or that part of it which 

 is secreted from the blood at times in which neither food nor 

 drink has been recently taken, and is applied especially to the 

 urine which is evacuated in the morning before breakfast. The 

 urina potus indicates the urine secreted shortly after the intro- 

 duction of any considerable quantity of fluid into the body ; 

 and the urina cibi the portions secreted during the period im- 

 mediately succeeding a meal of solid food. The last kind con- 

 tains a larger quantity of solid matter than either of the 

 others ; the first or second, being largely diluted with water, 

 possesses a comparatively low specific gravity. Of these three 

 kinds, the morning urine is the best calculated for analysis, 

 since it represents the simple secretion unmixed with the ele- 

 ments of food or drink ; if it be not used, the whole of the 

 urine passed during a period of twenty -four hours should be 

 taken. In accordance with the various circumstances above- 

 mentioned, the specific gravity of the urine may, consistently 

 with health, range widely on both sides of the usual average. 

 The average healthy range may be stated at from 1015 in the 

 winter to 1025 in the summer, and variations of diet and ex- 

 ercise may make as great a difference. In disease, the varia- 

 tion may be greater ; sometimes descending, in albumin uria, 

 to 1004, and frequently ascending in diabetes, when the urine 

 is loaded with sugar, to 1050, or even to 1060. 



The whole quantity of urine secreted in twenty-four hours is 

 subject to variation according to the amount of fluid drunk, 

 and the proportion of the latter passing off from the skin, 

 lungs, and alimentary canal. It is because the secretion of 

 the skin is more active in summer than in winter, that the 

 quantity of urine is smaller, and its specific gravity propor- 

 tionately higher. On taking the mean of numerous observa- 

 tions by several experimenters, Dr. Parkes found that the 

 average quantity voided in twenty-four hours by healthy 

 male adults from twenty to forty years of age, amounted to 

 fluid ounces. 



Chemical Composition of the Urine. 



The urine consists of water, holding in solution certain ani- 

 mal and saline matters as its ordinary constituents, and occa- 

 sionally various matters taken into the stomach as food 

 salts, coloring matter, and the like. The quantities of the 

 several natural and constant ingredients of the urine are 



