204 EXCRETION BY THE KIDNEYS AND SKIN 



compounds are normally very much more abundant in the portal 

 blood than in the arterial, but when the liver is removed they 

 are evenly distributed throughout the circulation, and the animal 

 dies in a few days of symptoms which can be aggravated by ad- 

 ministration of the ammonia compounds; all of which circum- 

 stances 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 out- 

 put of urea. Consequently this substance must be formed else- 

 where, but by what organs is unknown. It is not impossible 

 that it is formed to some extent in all organs where proteid dis- 

 sociation 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 full oxidized; it can be oxidized 

 outside the body. Thus the heat-producing capacity of the pro- 

 teids 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 dissociation is consumed in building up 

 the urea molecule to be discharged. 



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, be- 

 sides 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 con- 

 stituents 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. 



In some animals uric acid takes the place of urea, none of the 

 latter being formed. In these cases it is manufactured by the 

 liver from ammonia compounds. This does not, however, seem 

 to be the origin of uric acid in human urine. It has been looked 

 upon as unconverted urea, i. e., as a product antecedent to urea; 

 but at present such does not seem to be the case. A theory that it 



