I][ 4 Immunity 



mechanism either identical with or analogous to that by 

 which cellular nutrition is maintained, and points out that 

 in the case of methylene-blue and other colored substances, 

 which afford an opportunity to make ocular observations 

 upon the absorption of the pigment by the cells, only certain 

 cells absorb the colors. 



Cell nutrition is therefore probably carried on through the 

 agency of receptors by which appropriate nutrient hap- 

 tophorous groups are apprehended and utilized. 



"We now come to the important question of the signifi- 

 cance of the toxophile groups in organs. That these are in 

 function especially designed to seize on toxins cannot be for 

 one moment entertained. It would not be reasonable to 

 suppose that there were present in the organism many 

 hundreds of atomic groups, destined to unite with toxins, 

 when the latter appeared, but in function really playing no 

 part in the processes of normal life, and only arbitrarily 

 brought into relation with them by the will of the investi- 

 gator. It would, indeed, be highly superfluous, for example, 

 for all our native animals to possess in their tissues atomic 

 groups deliberately adapted to unite with abrin, ricin, and 

 crotin, substances coming from far-distant tropics." 



"One may, therefore, rightly assume that these toxophile 

 protoplasmic groups in reality serve normal functions in the 

 animal organism, and that they only incidentally and by 

 pure chance possess the capacity to anchor themselves to 

 this or that toxin." 



' ' The first thought suggested by this assumption was that 

 the atom group referred to must be concerned in tissue 

 change ; and it may be well here to sketch roughly the laws 

 of cell metabolism. Here we must, in the first place, draw 

 a clear line of distinction between those substances which 

 are able to enter into the composition of the protoplasm, and 

 so are really assimilated, and those which have no such 

 capacity. To the first class belong a portion of the food- 

 stuffs, par excellence; to the second almost all our pharma- 

 cological agents, alkaloids, antipyretics, antiseptics, etc." 



"How is it possible to determine whether any given 

 substance will be assimilated in the body or not ? There can 

 be no doubt that 'assimilation is in a special sense a synthetic 

 process that is to say, the molecule of the food-stuff con- 

 cerned enters into combination with the protoplasm by a 

 process of condensation involving loss of a portion of its 



