476 PHYSIOLOGY. 



neutral proteid of the blood. In the fasting salmon Miescher found 

 that the proteid of vanishing muscles was changed into the proteid of 

 the testicles which grew at that period. In starvation the heart-muscle 

 does not waste, but acquires its proteid from the other proteids of the 

 body. 



A cleavage by hydrolysis must precede every transformation of 

 proteid inside the body. 



The amino-acids and polypeptids enter the general circulation. 

 Leathes and Howell have found amido-acids in the blood. When the 

 amido-acids arrive at the tissue cells they undergo two changes : they 

 may be used as keystones in building up the tissue proteid, or they 

 may be broken up by the intracellular ferments, forming ammonia, 

 which is excreted as urea. When the proteids of the blood are in con- 

 tact with the cells the intracellular ferments break them up into poly- 

 peptids and build them into their own peculiar tissue. When the 

 polypeptids are injected into the circulation they do not appear in the 

 urine as polypeptids or in the shape of amido-acids, which formed 

 them, but probably as urea. In the breaking down of proteids by the 

 intracellular ferments we have the old amino-acids replaced by the new 

 building stones, the new amino-acids. These old amino-acids are 

 broken up into ammonia and changed into urea. In certain families 

 the amido-acids are not acted upon by the intracellular ferments ; then 

 you have cystinuria and alkaptonuria. In alkaptonuria the patient 

 excretes homogentisinic acid, which is derived from the amino-acids, 

 ty rosin and phenylalanin. One of the amino-acids, glycocoll, on its 

 way to be excreted, meets benzoic acid and forms hippuric acid. Grlyco- 

 coll may also unite with poisons in the blood in a like manner, taking 

 away their toxic properties and excreting them. Alanin and glyco- 

 coll, two amido-acids, when given increase the excretion of sugar ' in 

 pancreatic diabetes. In the metabolism of the body the amido-acids 

 occupy the front rank. 



Specific Dynamic Action of Proteids. 



Rubner believes that proteids stimulate the metabolism of the 

 body to a greater degree than carbohydrates or fats. Eubner found 

 that after taking meat in excess of starving metabolism, the specific 

 dynamic action caused a heat increase of 32.28 per cent. After inges- 

 tion of a smaller quantity the specific dynamic action was only 29.60 

 per cent. The average of these or 30.94 per cent, represents the 

 specific dynamic action of proteid or the increased heat production 

 after the ingestion of meat containing 100 per cent, of the energy- 



