430 EXCRETION 



and according to the quantity of drink and exercise have just been men- 

 tioned. The water of the urine is also liable to be influenced by the condi- 

 tion of the nervous system, being sometimes greatly increased, e.g., in hysteria 

 and in some other nervous affections, and at other times diminished. The 

 increase in water may be either attended with an augmented quantity of 

 solid matter in some diseases, as in ordinary diabetes, or may be nearly the 

 sole change, as in the affection termed diabetes insipidus. A febrile con- 

 dition almost always diminishes the quantity of water; and a like diminution 



is caused by any affection which draws off 

 a large quantity of fluid from the body 

 through any other channel than that of the 

 kidneys, e.g., the bowels or the skin. 



In disease or after the ingestion of special 

 foods, various abnormal substances occur in 

 urine, of which the following may be men- 

 tioned: Seralbumin, serum globulin, 

 enzymes (apparently some are present in 

 health also), proteoses, blood, sugar, bile 

 acids and pigments, casts, fats, various salts 

 FIG. 292. Crystals of Urea. taken as foods or as medicines, micro-organ- 

 isms of various kinds. 



The Nitrogenous Substances in Urine. The nitrogenous waste prod- 

 ucts which are formed in the body in the metabolism of the protein foods 

 are ultimately eliminated chiefly through the kidney, to some extent through 

 the bowel, and slightly through the skin. The total nitrogen in the urine 

 and in the feces multiplied by the factor 6.25 is a measure of the nitrogenous 

 foods, i.e., proteins, metabolized by the body. The nitrogen excreted in the 

 urine is in the form of urea 87 . 5 per cent., ammonia 4.3 per cent., kreatinin 

 3 . 6 per cent., uric acid o . 8 per cent., and undetermined forms 3.73 per cent., 

 according to Folin. The total quantity of nitrogen eliminated in all these 

 forms per day is given as about 18 grams. In Chittenden's experiments 

 this quantity is reduced to as low as 6 grams or even less per day. 



Urea. Urea, CON 2 H 4 , is the principal solid constituent of the urine, 

 forming nearly one-half of the total quantity. It is also the most important 

 ingredient, since it is the chief form in which the waste nitrogen which is 

 derived from protein metabolism is excreted from the body. 



Properties. Urea, like other solid constituents of the urine, exists in a 

 state of solution. When in the solid state, it appears in the form of delicate 

 silvery acicular crystals, which, under the microscope, are seen as four- 

 sided prisms, figure 292. It readily combines with some acids, like a weak 

 base, and may thus be conveniently procured in the form of crystals of nitrate 

 or oxalate of urea, figures 293 and 294. 



Urea is colorless when pure; when impure it may be yellow or brown. 



