THE KIDNEYS AND URINE. 357 



The variations of the water in different seasons, and according to the 

 quantity of drink and exercise, have already been mentioned. The water 

 of the urine is also liable to be influenced by the condition of the nervous 

 system, being sometimes greatly increased in hysteria, and some other 

 nervous affections; and at other times diminished. In some diseases it is 

 enormously increased; and its increase may be either attended with an aug- 

 mented quantity of solid matter, as in ordinary diabetes, or may be nearly 

 the sole change, as in the affection termed diabetes insipidus. In other 

 diseases, e.g. . the various forms of albuminuria, the quantity may be con- 

 siderably diminished. A febrile condition almost always diminishes the 

 quantity of water; and a like diminution is caused by any affection which 

 draws off a large quantity of fluid from the body through any other chan- 

 nel than that of the kidneys, e.g., the bowels or the skin. 



Method of estimating the Solids. A useful rule for approximately 

 estimating the total solids in any given specimen of healthy urine is to 

 multiply the last two figures representing the specific gravity by 2*33. 

 Thus, in urine of sp. gr. 1025, 2 '33x25 =58 '25 grains of solids, are con- 

 tained in 1000 grains of the urine. In using this method it must be 

 remembered that the limits of error are much wider in diseased than in 

 healthy urine. 



Variations in the Specific Gravity. The specific gravity of the 

 human urine is about 1020. Probably no other animal fluid presents so 

 many varieties in density within twenty-four hours as the urine does; for 

 the relative quantity of water and of solid constituents of which it is 

 composed is materially influenced by the condition and occupation of the 

 body during the time at which it is secreted, by the length of time which 

 has elapsed since the last meal, and by several other accidental circum- 

 stances. The existence 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 term urina potus indicates the urine 

 secreted shortly after the introduction of any considerable quantity of 

 fluid into the body: and the urina cibi, the portions secreted during the 

 period immediately 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 in health, since it represents the simple secretion 

 unmixed with the elements 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. 



