394 PHYSIOLOGY CHAP. 



synthetise hippuric acid are exclusively the kidneys, for when 

 these organs are excised, and benzoic acid and glycocoll injected 

 into the blood, the animal then being killed after 3-4 hours, there is 

 no trace of hippuric acid, either in the blood, or in the liver or 

 muscles, but, on the contrary, free benzoic acid is found. To this 

 negative proof that the kidneys formed hippuric acid by synthesis, 

 they added positive proof, by establishing artificial circulation 

 with defibrinated blood, to which they added glycocoll and benzoic 

 acid, in the freshly excised kidneys of a dog. Hippuric acid was 

 found to be present both in the blood that left the kidneys and 

 in the fluid that escaped from the ureters. The phenomenon 

 occurred equally when the blood was warmed to the temperature of 

 the body, and when it was cold. If benzoic acid only was added 

 to the blood, the amount of hippuric acid formed was less. 



The synthesis also took place partially when the kidney 

 was broken up into small pieces, steeped in the extracted blood to 

 which benzoic acid and glycocoll had been added, and then agitated 

 (Kochs) ; but if the kidney is reduced to a homogeneous pulp, so 

 as to exhaust the vitality of all its cells, or if a kidney excised 

 several hours previously is used, there will be no trace of hippuric 

 acid (Schrniedeberg and Bunge). It is clear that this synthesis 

 does not depend on specific chemical compounds in the renal 

 tissue, but on the metabolic activity of the surviving cells of the 

 excised kidney. 



No hippuric acid is formed when serum that has been entirely 

 deprived of corpuscles by the centrifuge is employed, instead of 

 circulating defibrinated blood containing benzoic acid and glyco- 

 coll in the kidney. The participation of the blood corpuscles is, 

 therefore, indispensable to the synthesis effected by the kidneys, 

 probably because they supply the oxygen. This is proved by the 

 fact that the synthesis also fails when the artificially circulated 

 blood has been previously saturated with carbon monoxide. 



If in dogs the kidneys alone have the power of effecting the 

 synthesis of hippuric acid, the same cannot be affirmed of other 

 animals. In fact, Schrniedeberg and Bunge saw a formation of 

 hippuric acid in frogs after the extirpation of the kidneys : 

 Salomon found hippuric acid in the blood, muscles, and liver of the 

 rabbit, after nephrectorny, when benzoic acid was introduced. 



We do not know whether the synthesis of hippuric acid takes 

 place in man exclusively by the kidneys, as in dogs, or by means 

 of other tissues also, as in rabbits. We only know that in renal 

 diseases in which there is a conspicuous degeneration of the 

 epithelia, a lesser amount of hippuric acid is formed, and if benzoic 

 acid be administered in these cases some of it reappears as such in 

 the urine (Stokvis, Kronecker). 



If benzoic acid is injected into birds, it does not, according to 

 Jaffe (1877), reappear as hippuric acid, but in combination with 



