220 ' EXCRETION. 



its of variation of its different constituents; and it has 

 been found necessary, in treating of the individual excre- 

 mentitious 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 will consider how far the 

 absolute quantities of the urinary principles and other ex- 

 crementitious substances represent the physiological waste 

 which is always coincident with the repair of parts. A full 

 and complete history of all the variations in the urine would 

 be inconsistent with the scope of this work. 1 



Variations with Age and Sex. There are decided dif- 

 ferences in the composition of the urine at different periods 

 of life and in the sexes. These must 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 variations, their re- 

 lations to the organism are not materially modified, except, 

 perhaps, at an early age ; and the influence of sex and age 

 is merely felt as they affect the diet and general habits of 

 life. 



It is stated by most authors that the urine of the foetus 

 is highly albuminous ' and contains no urea; but examina- 

 tions 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 researches of the authorities 

 on this subject, quoted by Parkes, 3 leave the question of the 

 composition of the urine in the foetus and during the first 



1 For more extended details of the variations of the urine in health and dis- 

 ease, the reader is referred to special treatises. Dr. Parkes considers these 

 points very fully. (PARKES, The Composition of the Urine in Health and Disease, 

 and under the Action of Remedies, London, 1859, pp. 39-179.) 



5 Op. tit., p. 41, etseq. 



