444 PHYSIOLOGY. 



oxalate, and crystallizes into flat or prismatic bodies. Both, types 

 of crystals may very readily be demonstrated by placing crystals of 

 urea beneath cover-glasses and allowing drops of nitric and oxalic 

 acids, respectively, to flow beneath the cover-glasses. After some 

 little time crystals of the respective types will be seen to form. 

 Besides being free, urea is found combined in the urine with sodium 

 chloride. 



DECOMPOSITION OF UREA. When urea is heated, vapors of 

 ammonia are evolved. Urine is also subject to an alkaline fermenta- 

 tion, due to the micrococcus urese. This generally follows the acid 

 fermentation, but may take place without it, in the bladder as well 

 as outside. This fermentation is accomplished by decomposition of 

 the urea into carbonate of ammonia. By virtue of this the urine is 

 strongly darkened, becomes alkaline, putrescent, and forms a film of 

 bacteria on its surface. Urinals always have an ammoniacal odor. 



Fig. 168. Micrococcus Uresje. X 500. (After VON JAKSCH.) 

 Hypobromite of soda decomposes urea as follows: 



SNaBrO = C0 2 + N 2 + 2H 2 + 3NaBr 



Una. Sodium Carbonic. Nitrogen. Sodium 



hypobromite. acid. bromide. 



Upon this reaction depends an estimation of the amount of urea 

 present in a sample of urine. The calculation is made in units of 

 nitrogen-gas, which gas rises in small bubbles to be collected and 

 measured. 



The constituents of urine are not actually formed in the kidney 

 itself, as loile is formed in the liver, but are formed elsewhere. The 

 kidney is simply the place where the constituents are picked out from 

 the blood and eliminated from the body. 



Muscular exercise has but a slight effect on the amount of urea 

 excreted ; this is in striking contrast to the quantity of carbonic acid 

 that accompanies muscular exertion to find exit in the expired air. 

 Muscle-work falls upon the carbon rather than upon the nitrogen of 

 the muscle-substance. 



QUANTITY OF UREA. The quantity of urea excreted daily 

 varies, but may be averaged as 500 grains. According to Tschlenoff, 



