VARIATIONS IN THE URESE. 223 



to note the most important of these variations and endeavor 

 to appreciate the conditions which combine to produce them, 

 assigning to each one its proper value. 



At different seasons of the year and in different climates, 

 the urine presents certain variations in its quantity and com- 

 position. It seems necessary that a tolerably definite quan- 

 tity of water should be discharged from the body at all 

 times ; and when the temperature or hygrometric condition 

 of the atmosphere is favorable to the action of the skin, as 

 in a warm, dry climate, the quantity of water in the urine is 

 diminished, and its proportion of solid matters correspond- 

 ingly increased. On the other hand, the reverse obtains 

 when the action of the skin is diminished from any cause. 

 This fact is a matter of common remark, as well as of scien- 

 tific observation. 



At different periods of the day, the urine presents con- 

 stant and important variations. It is evident that the spe- 

 cific gravity must be constantly varying with the proportion 

 of water and solid constituents. According to Dalton, the 

 urine first discharged in the morning is dense and highly col- 

 ored ; that passed during the forenoon is pale and of a low 

 specific gravity ; and in the afternoon and evening it is again 

 deeply colored, and its specific gravity is increased. 1 The 

 acidity is also subject to tolerably definite diurnal variations, 

 which have already been noted. 3 



Variations produced ~by Food. An immense number 

 of observations have been made upon the influence of ordi- 

 nary food, and upon diet restricted to particular articles. 

 These facts have necessarily been considered more or less 

 fully in connection with the origin of the urinary constit- 

 uents ; but it is important, in studying the influence of mus- 

 cular exercise, mental effort, etc., to constantly bear in mind 

 the variations occurring under the influence of the ingesta* 



1 D ALTON, A Treatise on Human Physiology, Philadelphia, 1867, p. 335. 



2 See page 190. 



