70 THE AMINO ACIDS 



their argument might be established. This they have 

 failed to do. 



DEAMINATION 



The failure to demonstrate the presence of amino 

 acids in the blood of the higher animals during diges- 

 tion led to the conception that the amino acids are 

 deaminated, that is, ammonia is split off while passing 

 the intestinal wall, this deamination being regarded as 

 the first stage in the catabolism of the amino acids. 

 This possibility was suggested by the work of Cohn- 

 heim upon certain of the lower forms of animal life 

 in which he showed the giving off of ammonia by the 

 intestine after addition of amino acids, and derived 

 support from the older work of Nencki and others 

 who showed that the ammonia content of the portal 

 blood was greater than that of the arterial during 

 digestion. It has been assumed that as result of this 

 process of deamination the ammonia split off is trans- 

 formed by the liver into urea and so quickly eliminated 

 by the kidneys. Such a view has been adopted as 

 explanatory for the long known rapid rise in urea 

 excretion following protein ingestion. 



It has been shown by Lang that deamination is a 

 property of a great many tissues of the body but it is 

 probable that certain of them possess a selective action 

 in this respect for some tissues deaminate certain of the 

 amino acids much more readily than others. In par- 

 ticular the intestine and liver seem to possess this 

 action in a high degree. To the liver a great import- 



