408 PKACTICAL PHYSIOLOGY 



information regarding the breakdown of protein in the body. The 

 main function of the kidneys is to serve as a regulator of the composi- 

 tion of the blood, removing from it any excess of its normal constituents, 

 water, dextrose, sodium chloride, etc., and also injurious waste pro- 

 ducts, such as urea, uric acid, etc. The capacity of the kidneys for 

 their work can be determined most readily by the examination of the 

 urine. When the kidneys, or other parts of the urinary tract, are 

 diseased, abnormal substances, such as proteins, blood, pus cells, etc., 

 are mixed with the urine and can be detected in it in a more or less 

 changed state, according to the site of the lesion. 



In studying the chemistry of the urine, therefore, we must ascertain, 

 firstly, the nature of its various constituents and of their precursors in 

 the blood and tissues ; secondly, the total amount of those excretory 

 products which contain the nitrogen of the decomposed proteins ; and 

 thirdly, we must look for unusual products, indicating improper 

 composition of the blood or organic disease of the urinary tract. 



We must remember that the quantity and the composition of the 

 urine vary considerably within the limits of health, and in order to 

 form reliable conclusions we must collect the total urine for a period of 

 twenty-four hours. Even with a fair sample thus obtained, we must 

 consider the intake and loss of water ; copious drinking will increase 

 the quantity and lower the specific gravity of the urine ; on the other 

 hand, profuse sweating or diarrhoea will have the opposite effect. The 

 nature of the diet in relation to the reaction of the urine and the 

 quantity of urea must also be considered. 



GENERAL CHARACTERS OF URINE. 



Quantity. A healthy man of average weight (65-70 kg.) and height, 

 and living on an ordinary mixed diet, excretes about 1500 c.c. per 

 24 hours. If we wish to ascertain whether any one of its constituents 

 is being excreted in normal amount, a knowledge of the total daily 

 excretion of urine is indispensable, a mere determination of the 

 percentage in an isolated sample being of very slight value. For 

 accurate work (e.g. in making observations in metabolism) the method 

 employed is to collect the total urine for the 24 hours in a suitable 

 vessel, and then to remove from this a measured sample for analysis. 1 



1 In doing this, the bladder is emptied at some chosen hour (best in the morn- 

 ing), and this urine thrown away ; all urine passed subsequently to this is 

 collected in a sterile flask or bottle containing a few c.c. of chloroform, and at 

 the same hour next day the bladder is again emptied and the urine added to the 

 twenty-four hour specimen. When the observation is being conducted on the 

 lower animals, it is usually necessary to employ the catheter. 



