ELEMENTARY CHEMICAL PHYSIOLOGY 251 



If a large excess of water is added to the above a precipitate is 

 thrown down. If this be dissolved in a little caustic soda, a solu- 

 tion of hsematoporphyrin in an alkaline medium is obtained, which 

 shows a four-banded spectrum when examined, the positions of 

 the bands being I 630, A 580, A 550, and A 520 approximately 

 (Spectrum 11 hi Chart). 



Hsematoporphyrin may be regarded as iron-free haematin, and 

 identical in composition with bilirubin. 



Solutions of hsematoporphyrin exhibit a red fluorescence. This 

 pigment must be regarded as normally present in small quantities 

 in urine. 



CHAPTER XIII 

 URINE 



In studying the chemistry of the urine, 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 1,500 c.c. 

 per twenty-four 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 deter- 

 mination of the percentage in an isolated sample being of very 

 slight value. For accurate work the method employed is to collect 

 the total urine for the twenty-four hours in a suitable vessel, 

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

 The amount of urine is increased by the imbibition of large quantities 



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

 morning), 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 th'e lower animals, it is usually necessary to employ the catheter. 



