426 EXCRETION. 



Variations in the Composition of the Urine. 



The urine represents, in its varied constituents, not only a great part of the physiolo- 

 gical disintegration of the organism, but it contains elements evidently derived from the 

 food. Its constitution is varying with every different condition of nutrition, with exer- 

 cise, 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 sys- 

 tem. There is no fluid in the body that contains such a variety of principles, as a con- 

 stant condition, but in which the proportion of these principles is so variable. It is for 

 this reason that we have given in the table of the composition of the urine the ordinary 

 limits of variation of its different constituents ; and it has been found necessary, in treat- 

 ing of the individual excrementitious principles, to refer to some of the variations in their 

 proportion in the urine. In treating more specially of the physiological variations of the 

 urine, we shall only refer in general terms to conditions that produce wide and important 

 changes in the proportion of its constituents ; and, under the head of nutrition, we shall 

 consider how far the absolute quantities of the urinary principles and other excrementi- 

 tious substances represent the physiological waste which is always coincident with the 

 repair of the parts. 



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 upon the different conditions, of nutrition and exercise, and in part upon differences 

 in the food. Although the quantities of excrementitious matters present great varia- 

 tions, 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 is stated by most authors that the urine of the foetus is highly albuminous and con- 

 tains no urea ; but examinations of the urine in the foetus and newly born have been so 

 few that we know very little regarding its constitution and normal variations. The re- 

 searches of the authorities on this subject, quoted by Parkes, leave the question of the 

 composition of the urine in the foetus and during the first days of extra-uterine life 

 still uncertain. In a specimen of urine taken from a still-born child delivered with for- 

 ceps, examined by Drs. Elliot and Isaacs, the presence of urea was determined. Dr. 

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



With our present imperfect knowledge of the composition of the urine at the earliest 

 periods of existence, it is impossible to deduce any conclusions regarding the production 

 of the excrementitious principles at this time ; and it would be unprofitable to detail the 

 unsatisfactory and conflicting examinations to be found in works devoted specially to the 

 urine. Observations upon children between the ages of three and seven are more definite. 

 At this period of life, the amount of urea excreted in proportion to the weight of the body 

 is about double that in the adult. The amount of chlorine in children is about three 

 times the quantity in the adult ; and the proportionate amount of other solid matters is 

 also greater. The amount of water excreted by the kidneys in children, in proportion 

 to the weight of the body, is very much greater than in the adult, being more than 

 double. From eight years of age to eighteen, the urinary excretion becomes gradually 

 reduced to the adult standard. It has been observed that crystals of oxalate of lime 

 are much more frequent in the urine of children between four and fourteen years of 

 age than in the adult. 



There are not many definite observations on record upon the composition of the urine 

 in the later periods of life. It has been shown, however, that there is a decided dimi- 

 nution, at this time, in the excretion of urea, and that the absolute quantity of urine is 

 somewhat smaller. 



The absolute quantity of the urinary excretion in women is less than in men, and the 



