GASES OF THE URINE. 425 



the proportion of oxygen being very much greater. These facts point to the probability 

 of the formation of urrosacine from heemaglobine. 



The quantity of coloring matter in the normal urine is very small. It is subject to 

 considerable variation in disease, and almost always it is fixed by deposits and calculi of 

 uric acid or the urates, giving them their peculiar color. This principle first makes its 

 appearance in the urine and is probably formed in the kidneys. So little is known of its 

 physiological or pathological relations to the organism, that it does not seem necessary to 

 follow out all of the chemical details of its behavior in the presence of different reagents. 



The normal urine always contains a small quantity of mucus, with more or less epi- 

 thelium from the urinary passages, and a few leucocytes. These form a faint cloud in 

 the lower strata of healthy urine after a few hours' repose. The properties of the differ- 

 ent kinds of mucus have already been considered. An important peculiarity, however, 

 of the mucus contained in normal urine is that it does not seem to excite decomposition 

 of the urea, and that the urine may remain for a long time in the bladder without under- 

 going any putrefactive change. 



Gases of the Urine. 



In the process of separation of the urine from the blood by the kidneys, a certain 

 proportion of the gases in solution in the circulating fluid is also removed. For a long 

 time, indeed, it has been known that the normal human urine contained different gases, 

 but lately some very interesting observations on this subject have been made by M. 

 Morin, in which the proportions of the free gases in solution have been accurately esti- 

 mated. By using the method employed by Magnus in estimating the gases of the blood, 

 Morin was able to extract about two and a half volumes of gas from a hundred parts of 

 urine. By careful experiments, he ascertained that a certain quantity of gas remained in 

 the urine and could not be extracted by his ordinary process. This amounted to about 

 one-fifth of the whole volume of gas. Adding this to the quantity of gas extracted, he 

 obtained the proportions to one litre of urine, in cubic centimetres, which are given in 

 the table, viz. : 



Oxygen 0-824 



Nitrogen 9'589 



Carbonic acid 19'620 



These proportions represent the average of fifteen observations upon the urine secreted 

 during the night. 



The proportion of these gases was found by Morin to be subject to certain variations. 

 For example, after the ingestion of a considerable quantity of water or any other liquid, 

 the proportion of oxygen was considerably increased (from 0'824 to 1'024), and the car- 

 bonic acid was diminished more than one-half. The most interesting variations, how- 

 ever, were in connection with muscular exercise. After walking a long distance, the 

 exercise being taken both before and after eating, the quantity of carbonic acid was found 

 to be double that contained in the urine after repose. The proportion of oxygen was 

 very slightly diminished, and the nitrogen was somewhat increased. The variations of 

 these gases, however, were insignificant. 



Morin explains the great increase in the proportion of carbonic acid, by the greater 

 respiratory activity during exercise. It is well known, indeed, that muscular exercise 

 largely increases the proportion of carbonic acid in the blood and the quantity eliminated 

 by the lungs; and, as the carbonic acid of the urine is undoubtedly derived from the 

 blood, we should expect that the same conditions would increase its proportion in this 

 secretion. 



It is not probable that the kidneys are very important as eliminators of carbonic acid 

 from the system, but it is certain that the presence of this gas in the urine assists in the 

 solution of some of the saline constituents of this fluid, notably the phosphates. 



