336 PHYSIOLOGY CHAP. 



albuminoid degeneration of the epithelia, due to accumulation in 

 the blood of toxic waste-products. 



The urine of operated as compared with normal dogs proved to 

 contain carbamic acid, which was either entirely absent in normal 

 urine (Drechsel and Abel) or occasionally present in minute 

 quantities (Hahn and Nencki). The urine of the operated dogs 

 further showed a distinct reduction in the urea content, 

 associated with a constant increase of uric acid and ammonia. 

 These facts, which agree with the theory that the greater part of 

 the urea is formed in the liver, show that in all probability a 

 considerable part, if not the whole, of the carbamic acid is a 

 product of the conversion of nitrogenous substances effected by the 

 spleen, pancreas, and walls of the intestinal tract, which, when 

 normally conveyed to the liver by the portal system, gives rise to 

 the formation of urea. 



Nencki, Pawlow, and Zaleski (1896) arrived at very important 

 results in a series of observations on the ammonia content of the 

 blood and other organs, and the formation of urea in mammals. 

 They found that the portal blood in dogs fed on flesh contains 

 five times as much ammonia as arterial blood, twice as much as 

 venous blood. On the other hand, the ammonia content of the 

 blood of the hepatic veins is approximately equal to that of 

 arterial blood. They further showed that the amount of ammonia 

 varies in the blood of the different roots of the portal system ; it 

 is maximal in the gastric mucous membrane, and largely exceeds 

 the quantity found in the contents of the stomach. On the other 

 hand, the ammonia content of the intestinal mucous membrane 

 and of the intestinal contents is approximately the same. It 

 diminishes in starvation, and still more on a mixed non-flesh 

 diet of bread and milk. Ammonia seems to be a metabolite 

 of the digestive glands, because the same quantity is found in 

 the gastric mucosa of a dog fed abundantly on flesh, and of 

 another dog, with a gastric and oesophageal fistula, subjected to 

 " sham feeding." Lastly, these experimenters found in a dog 

 with Eck's fistula that the ammonia content of the blood increases 

 to a marked extent during a flesh diet (as compared with a diet 

 of bread and milk), this increase becoming larger in proportion as 

 the symptoms of auto-intoxication are aggravated. 



From their results as a whole these authors concluded that 

 owing to the function of the gastric and intestinal glands 

 (including the pancreas), an enormous amount of ammonia is 

 produced, which is stored up in the liver, where it is converted 

 into urea. According to them, the larger part, if not the whole, 

 of the urea originates in the metabolism of the glands, which 

 differs from that of the muscles, the liver being thus the most 

 efficient defence of the body against intoxication due to ammonia 

 and carbamic acid. 



