74 THE PROTEOMORFHIC THEORY AND THE NEW MEDICINE 



in this infinitesimal quantity seems necessary to the very life of 

 the organism, light is thrown from yet another direction on the 

 intricate co-ordinations of the animal machine as effected with 

 the aid of the nitrogen-bearing molecule. 



Here is a substance which, were we able to remove but two 

 of its hydrogen atoms, would become merely a commonplace 

 member of the group of amino-acids, ready to be taken up by 

 this, that, or the other tissues of the body, as a component part 

 of its protein ; and yet, in virtue of the presence of those two 

 supernumerary hydrogen atoms, it gains special affinity for cells 

 of a particular type, and causes those cells, in recombining their 

 structural materials, to undergo a destructive metabolism of 

 an almost explosive type which finds 'tangible expression in a 

 muscular contraction. 



Could we look into the structure of the muscle cells during 

 this time of its explosive activity, with vision more ultra-micro- 

 scopic than is afforded by any instrument yet devised, we should 

 see that the cell, in readjusting its molecules, has some left-over 

 materials, like the shavings and sawdust of a carpenter, that 

 are not needed in the new combinations; and that these left- 

 over products are excreted into the surrounding fluid medium. 

 And what is true of the muscle cell under these circumstances 

 is equally true of every other muscle cell whenever it contracts 

 from whatever cause, and of the cells of every other bodily tissue 

 when they undergo characteristic activities. Changes in the molec- 

 ular structure of the cell incident to or underlying all activity 

 are affected only at the expense of potential energy, and with 

 actual gain or lo'ss of physical material. Destructive metamor- 

 phoses, which attend the active functioning of all tissues, are 

 attended by a loss of substance. And it is almost axiomatic to 

 say that the precise character of the substance given out as a 

 waste product or a by-product must be dependent on the char- 

 acter of the substance available to replace it. On occasion there 

 comes to hand, let us say, a group of atoms that is admirably 

 suited to fit into the structure of the molecule of the cell, pro- 

 vided that another group similar in character, but, on the whole, 

 somewhat less satisfactory is excluded. So the substitution is 

 made, and the discarded group of atoms flows away in the blood 

 stream. 



It is obvious that groups of atoms that can thus be substituted 

 one for the other may bear to each other a certain complementary 

 relation. It is one way of expressing this relation to say that 

 the intruding molecule is an antigen, and that the extruded one 

 is an antibody. In view of the mutual relations of these struc- 

 tures, it does not seem strange that members of the two clans, 

 when they chance to meet in the blood stream, can enter into 



