METABOLISM, NUTRITION AND DIETETICS 437 



and elsewhere partially changed into the other. But there 

 is some evidence that serum-albumin is more directly related 

 to the proteids of the food than serum-globulin. And it 

 is said that during starvation the albumin is relatively 

 diminished, and the globulin relatively increased. However 

 this may be, it cannot be doubted that the conversion of 

 peptones, directly or indirectly, into the proteids of the 

 blood-plasma forms the first recognisable step in the trans- 

 formation of the greater part of the digested proteids. 



Living and Dead Proteids. Now and again a living proteid 

 molecule in the whirl of flying atoms which we call a muscle-fibre, 

 or a gland-cell, or a nerve-cell, falls to pieces. Now and again a 

 molecule of proteid, hitherto dead, coming within the grasp of the 

 molecular forces of the living substance, is caught up by it, takes on 

 its peculiar motions, acquires its special powers, and is, as we phrase 

 it, made alive. But it is not any difference in the kind of proteid 

 which determines whether a given molecule shall become a part of 

 one tissue rather than of another. For it is from the serum-albumin 

 and serum-globulin of the blood that all the proteid material required 

 to repair the waste of the body must ultimately be derived ; and a 

 particle of serum-albumin may chance to take its place in a liver-cell 

 and help to form bile, while an exactly similar particle may become 

 a constituent of an endothelial scale of a capillary and assist in 

 forming lymph, or of a muscular fibre of the heart and help to drive 

 on the blood, or of a spermatozoon and aid in transferring the 

 peculiarities of the father to the offspring. Indeed, although there 

 are differences of detail, the broad lines of nutrition are the same for 

 all tissues ; and just as a tomb and a lighthouse, a palace and a 

 church, may be, and have been built with the same kind of material, or 

 even in succession with the very same stones, so every organ builds up 

 its own characteristic structure from the common quarry of the blood. 



In the case of the more highly developed tissues at least, no mere 

 change of food will radically alter structure. A cell may be fed with 

 different kinds of food, it may be over-fed, it may be ill-fed, it may 

 be starved ; but its essential peculiarities remain as long as it con- 

 tinues to live. But in proportion as the advance of physiology has 

 emphasized the dominant position of organization, it has taken away 

 the hope of our ever being able to understand in what it is that the 

 difference between the living and the dead cell, between living and 

 dead proteid, or protoplasm, really consists. 



The speculation of Pfliiger, that the nitrogen of living proteid 

 exists in the form of cyanogen radicals, whilst in dead proteid it 

 is in the form of amides, and that the cause of the characteristic 

 instability of the living substance its prodigious power of dissocia- 

 tion and reconstruction is the great intramolecular movement of 

 the atoms of the cyanogen radicals, is very interesting and ingenious, 

 but it remains, and is likely to remain, a speculation. And the same 



