THE ORGANIC CONSTITUENTS OF THE URINE. 239 



moreover, symptoms of carbamic-acid poisoning are observed when 

 the liver is excluded from the general circulation, and, as has been 

 shown, the formation of urea from ammonium lactate or carbonate 

 may be demonstrated in the isolated livers of dogs. 



More recently Folin has advanced another hypothesis regarding 

 the origin of urea and the form in which the muscle nitro- 

 gen at least leaves the tissues, which seems fair to replace the 

 older views. According to the hypothesis of Voit, albumin 

 exists in the body in two forms, viz., as organized albumin, 

 which is built up into tissues, and as so-called circulating albumin, 

 which is present in excess of Avhat is actually required. Voit 

 further taught that the circulating albumin is broken down in the 

 tissues at large through the special activity of the living protoplasm, 

 but without becoming an integral part of the cells before its destruc- 

 tion. Pfliiger, on the other hand, took the contrary view, according 

 to which the circulating albumin must become part and parcel of 

 the cell before it can undergo katabolic disintegration. In either 

 event, however, it was assumed that the resulting nitrogenous 

 product appeared in the urine in the form of urea. Folin distin- 

 guishes sharply between tissue or endogenous metabolism, which 

 tends to be constant according to his investigations, and exogenous 

 or intermediate metabolism, which is variable. He regards krea- 

 tinin as the essential nitrogenous end-product in the first instance, 

 and finds that its elimination is practically constant for one and the 

 same individual. Urea, on the other hand, according to Folin's 

 concept, is the principal nitrogenous end-product of the exogenous 

 metabolism. It results in such manner that the amino-acids which 

 are formed during pancreatic digestion, in so far as they are not 

 needed to make up for tissue loss of nitrogen, are at once desami- 

 dized in the liver ; the non -nitrogenous remainder is then utilized 

 in the formation of fats and carbohydrates, while the amino group 

 gives rise to the formation of urea. In this manner the presence of 

 the large amounts of ammonium compounds which are found in the 

 portal blood during digestion is also well explained. But as Howell 

 remarks : While a portion and perhaps even a larger portion of the 

 urea arises from this early hydrolysis of the proteins of the food, 

 we must admit also that ammonium compounds may be formed in 

 the tissues of the body generally, probably by a similar process of 

 hydrolysis, followed by oxidation. This would suggest itself espe- 

 cially under pathological conditions, where the amount of urea 

 nitrogen may be in excess of that corresponding to the ingested 

 food. 



The total urinary nitrogen is under normal conditions practically 

 equivalent to the quantity ingested, barring the small fraction which 

 escapes digestion in the feces. Such a condition is spoken of as the 

 nitrogenous equilibrium of the body. Of this different levels may 

 exist, which may vary in the same individual. If the amount of 

 nitrogenous food is thus diminished, the amount of urinary nitrogen 



