310 HUMAN PHYSIOLOGY 



Alcohol. Alcohol when taken is absorbed rapidly 

 and rather quickly oxidized. It yields up heat and gives 

 rise to carbon dioxid and water. It is not known to be 

 transformed in fat or glycogen so there is no apparent 

 provision for its storage. The familiar fattening effect 

 of alcoholic drinks is indirect. It can be referred to two 

 circumstances: in the first place moderate drinking 

 creates a keen appetite and so favors overeating; 

 second, when alcohol is oxidized in the body there is less 

 call for the oxidation of fat or carbohydrate to meet the 

 current need. Fat is thus " spared" to accumulate, or 

 carbohydrate to be transformed into it. 



Nitrogenous Metabolism. An equivalent for this 

 title would be The History of the Amino-acids. No one 

 can pursue this subject far without the fullest command 

 of the facts of biochemistry. Our treatment must be 

 condensed and admittedly superficial. We have said 

 that the amino-acids are the structural units, the " build- 

 ing stones," of protein. What we call a single protein, 

 for instance, the albumin of white of egg, yields a con- 

 siderable number of amino-acids when it is thoroughly 

 digested. The total number known is about twenty. 



These diverse substances pass from the intestine into 

 the portal blood-stream. It was once held that they 

 were immediately combined to form proteins of the 

 types native in the plasma This is no longer believed; 

 while there must be some synthesis of new proteins 

 from the amino-acids it seems to be quite limited. Of 

 course it must be greater during the period of growth than 

 it is in a body which is no longer increasing in size. It 

 never ceases entirely for the proteins of the muscles and 

 glands are subject to a gradual disintegration so long as 

 life lasts and the losses need to be made good. 



According to one conception the proteins of the plasma 

 are offered to the tissues and appropriated by them as 

 may be required. To turn the proteins of the blood into 

 those of muscles it has been supposed that a local diges- 

 tion is carried on and the amino-acids combined accord- 



