164 INTERMEDIATE METABOLISM 



2. Estimation of Amino-acids in Blood 



Sorensen's method. — This depends upon the fact that 

 amino-acids on treatment with aldehydes midergo this 

 change. 



R R 



NH2— C— COOH + HCHO ~> CH2 : N— C— COOH + H2O. 



The NH2 group being thus destroyed, the resulting 

 product behaves as a true acid and can be estimated by 

 titration. 



By the use of these methods it has been shown that the 

 blood even in the fasting condition always contains amino- 

 acids, (3-5 mg. per 100 c.c), and the tissues from five to 

 ten times as much as the blood. During protein digestion 

 the amino-acid content rises in the general circulation, 

 and rises still more in the portal vein. But at the same 

 time there is no accumulation of amino-acids either in the 

 hver or in the other tissues. As regards the hver, the 

 amino-acids are evidently converted into some other form ; 

 they are either destroyed or synthesised into more complex 

 bodies. 



When a certain quantity of amino-acids is injected into 

 the blood it rapidly disappears. Part is excreted by the 

 kidneys either unchanged or as urea, but the remainder is 

 absorbed by the tissues. In the hver there is a rapid rise, 

 followed by a fall. In the other tissues the rise is more 

 gradual and soon reaches a maximum, which is maintained 

 for a considerable time. Simultaneously there is a rise in 

 the urea of the blood, setting in before the tissues have 

 become saturated with amino-acids. 



Confirmatory evidence against the absorption of foreign proteins 

 without preparatory hydrolysis is found in the remarkable reaction 

 known as anaphylaxis. When a protein is injected into the blood 



