204 EXCRETION BY THE KIDNEYS AND SKIN 



mm carbamate seems the typical compound, but ammonium 

 carbonate and others are probably likewise converted. Ar- 

 tificial circulation of these compounds through the liver gives 

 rise to urea; removal of the liver increases the ammonia 

 compounds and decreases the urea in the urine ; ammonia 

 compounds are normally very much more abundant in the 

 portal blood than in the arterial, but when the liver is re- 

 moved they are evenly distributed throughout the circula- 

 tion, and the animal dies in a few days of symptoms which 

 can be aggravated by administration of the ammonia com- 

 pounds; all of which circumstances go to show that it is 

 ammonia compounds which the tissues produce, and that 

 they are changed to urea in the liver. 



Still, removal of the liver does not suspend entirely the 

 output of urea. Consequently this substance must be formed 

 elsewhere, but by what organs is unknown. It is not impos- 

 sible that it is formed to some extent in all organs where 

 proteid dissociation is progressing. This is practically, if 

 not really, the case in health at any rate, even under the 

 theory above mentioned. 



It is to be noted that urea is not fidl oxidized; it can be 

 oxidized outside the body. Thus the heat-producing capac- 

 ity of the proteids is not completely utilized. If they have 

 been broken down in the body into substances simpler than 

 urea, then the amount of heat liberated in such dissocia- 

 tion is consumed in building up the urea molecule to be dis- 

 charged. 



Uric acid is combined in normal urine to form the urates 

 of sodium, potassium, magnesium, calcium and ammonium. 

 The urate of sodium is by far the most abundant of these, 

 and, besides urate of potassium, only traces of the others 

 are found. Free uric acid in human urine is pathological. 

 The urates, like urea, come ultimately from oxidation of the 

 nitrogenous constituents of the body. They are not formed 

 in the kidney, but pass out as such from the blood. About 

 9-14 gr. are discharged daily. The amount is increased in 

 gout. 



