352 EXCRETION 



absorption of oxygen; and carbon dioxide probably is useful in increas- 

 ing the solvent properties of the liquids of the organism. 



Variations in the Composition of the Urine. The urine not only 

 represents, in its varied constituents, a great part of the physiological 

 disintegration of the organism, but it contains matters evidently derived 

 from food. Its constitution is varying with different conditions of 

 nutrition, with exercise, bodily and mental, with sleep, age, sex, diet, 

 respiratory activity, the quantity of cutaneous exhalation, and, indeed, 

 with every condition that affects any part of the system. There is no 

 liquid in the body that presents such a variety of constituents as a con- 

 stant condition, but in which the proportion of these constituents is so 

 variable. It is for this reason that in the table of the composition of 

 the urine, the ordinary limits of variation of its different constituents 

 have been given ; and it has been found necessary, in treating of the 

 individual excrementitious products, to refer to some of the variations 

 in their proportion in the urine. 



Variations with Age and Sex. There are decided differences in 

 the composition of the urine at different periods of life and in the sexes. 

 These undoubtedly depend in part on the different conditions of nutri- 

 tion and exercise and in part on differences in the food. Although the 

 quantities of excrementitious matters present great variations, their 

 relations to the organism are not materially modified, except, perhaps, 

 at an early age ; and the influence of sex and age operates merely as 

 these conditions affect the diet and the general habits of life. 



It has been stated that urea does not exist in the urine of the foetus ; 

 but in a specimen of urine taken from a stillborn child delivered with 

 forceps, examined by Elliot and Isaacs, the presence of urea was deter- 

 mined. Beale found urea in a specimen taken at the seventh month. 

 Observations on children between the ages of three and seven have 

 shown that at this period of life, the urea excreted in proportion to 

 the weight of the body is about double the quantity excreted by the 

 adult. 



There are not many definite observations on record in regard to the 

 composition of the urine in the later periods of life. It has been shown, 

 however, that there is a decided diminution at this time in the excretion 

 of urea, and that the absolute quantity of urine is somewhat less. 



The Absolute quantity of solids excreted is less in women than in 

 men, and the same is true of the quantity in proportion to the weight 

 of the body ; still, the differences are not very marked, and the pro- 

 portion of the urinary constituents being subject to modifications from 

 the same causes as in men, the small deficiency, in the few direct obser- 

 vations on record, may be in part if not entirely explained by the fact 



