VII 



KATABOLIC CONSTITUENTS OF UKINE 



381 



e.g. (which under both normal and pathological conditions is 

 always less than that of distilled water), is increased by mineral 

 salts, and diminished by organic substances, such as bile salts. 

 The addition of bile to urine causes a perceptible alteration in its 

 surface tension, even with a concentration so low that chemical 

 tests are not perceptible (supra, p. 145). 



The determination of surface tension in any given fluid is most simply 

 ascertained by counting the number of drops required for 1 c.c. of the fluid to 

 fall drop by drop from a pipette. The number of drops is inversely pro- 

 portional to the magnitude of surface tension. 



The chemical composition of urine, both in man and animals, is 

 very complete, as shown by the number of individual substances 

 that can be chemically isolated, and recognised in it. The majority 

 of these, however, are present in such minute quantities under 

 normal conditions that a large amount of urine is required before 

 even a trace of them can be detected. 



Only a limited number of organic and mineral substances are 

 found dissolved in the urine in any appreciable quantity. Among 

 the former urea enormously predominates; next follow uric acid 

 and creatinine, but in much smaller amount: among the latter, 

 sodium chloride predominates, and the sulphates and the alkaline 

 and earthy phosphates are the other principal constituents. 



The following table will assist us in realising the quantitative 

 relations between the principal constituents of the urine, and the 

 maximal extent to which they vary with the diet. It gives the 

 analyses obtained by Bunge (1887) from a healthy youth, whose 

 total urine secreted in the 24 hours was collected, on an exclusively 

 flesh, and on an exclusively vegetable diet ; the former consisted of 

 veal seasoned with common salt, the latter of wheat bread with a 

 little butter and salt. To these data are added the averages 

 obtained by Parkes, under normal conditions, with an ordinary 

 mixed diet. 





