PROTEIN REGENERATION 19 



the food which it demands. As Leathes neatly puts it " the proteins 

 circulating in the blood are a currency which is not legal tender ". 



Abderhalden, among the modern workers, has been the most active 

 in upholding the view that a synthesis takes place in the intestinal 

 wall immediately after absorption, and that therefore all the material 

 is sent on into the animal organism in the form of coagulable protein. 

 Abderhalden and his co-workers hold further that the protein, which 

 is formed, is a neutral protein, probably serum protein. 



They depend for their evidence very largely on the fact that the de- 

 composition products of the protein have not in their opinion been clearly 

 demonstrated to be present in the blood. Abderhalden, however, ad- 

 mits that the present methods for the estimation of small amounts of 

 amino acids are very unsatisfactory. 



If there be no immediate synthesis to protein, then the building 

 material must be carried in a soluble form in the portal blood, and 

 then distributed in the blood stream to the tissues of the body in 

 order that these may take the material they require to satisfy their 

 immediate wants. Neither those who contend that there is immediate 

 resynthesis, nor those who adhere to the view that the material is 

 absorbed from the intestine in an amino acid form, conveyed in the 

 portal stream to the liver, possess evidence which is universally ac- 

 cepted. 



If, on the one hand the presence of amino acids has never been 

 satisfactorily demonstrated in the portal blood, there is no evidence 

 on the other hand of the increase of coagulable protein in the same 

 blood, such as would be demanded by the hypothesis of immediate 

 resynthesis. 



The great difficulty in reaching a final settlement of this question 

 arises from the fact that, on account of the rate at which the blood 

 flows through the intestinal vessels, the absorbed material is removed 

 extremely rapidly and is present in so small an amount ; a given amount 

 of blood at a given moment contains only mere traces of the material to 

 be tested for. Further it must be remembered, that the digestion and 

 setting free of the soluble digestion products is not explosive in char- 

 acter but is a gradual process thus limiting the amount of material 

 available for absorption. A number of estimations of the rate of in- 

 testinal blood flow have now been made. Cybulski (103) measured 

 the rate of flow through the portal vein of a dog which weighed 9-5 

 kilos, and found the rate of blood flow to be about 9000 c.c, per hour or 

 about 1 5oc.c. per minute. Burton Opitz (82) found in his experiments, 

 on the rate of the blood flow in the portal vein of dogs, that the mean 



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