72 THE AMINO ACIDS 



this regard is especially to be considered, correlated 

 as it has been with the explanation of the form in 

 which protein digestion products are absorbed. 



The recent observations of Folin and Denis and 

 others have rendered untenable the hypothesis that 

 deamination by the intestine is the first stage in the 

 catabolism of amino acids. They demonstrated that 

 during the absorption of amino acids from the intes- 

 tine there was no increase in ammonia or urea of the 

 blood and they further showed that the ammonia of 

 the portal blood is produced in large measure by the 

 products of putrefaction in the large intestine. The 

 retirement of the theory of intestinal deaminization 

 to account for the apparent absence of amino acids in 

 the blood carries with it also the untenability of the 

 idea that the liver is specifically concerned in the 

 formation of urea. To quote the authors: "In the 

 absence of satisfactory proof that deaminization and 

 urea formation is localized we are not justified in 

 assuming that the process is a specialized process in 

 the sense of being confined to some particular organ. 

 In other words, so far as we yet know, the urea form- 

 ing process is a characteristic of all the tissues and by 

 far the greatest amount of urea is therefore prob- 

 ably formed in the muscles. The negative results, 

 so far as any localized urea formation is concerned, is 

 almost satisfactory proof that there is none, for if 

 there were one central focus from which all or nearly 

 all of the urea originated we could scarcely have 

 failed to find it." 



