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Dr. Paul Ehrlich. 



lethal, whether given by intracerebral or by subcutaneous injection ; 

 for rabbits, however, the lethal dose was twenty times greater sub- 

 cutaneously than it was in intracerebral injection. This can only be 

 explained in the terms of Donitz's observation, viz., that in the case 

 of direct injection of the toxine into the brain, the toxophile atom 

 groups there present at once seize on all the toxine, while when the 

 toxine is administered through the blood stream, the toxophile groups 

 present in other organs also take up the toxine in equivalent quanti- 

 ties. In the case of rabbits the absorption of the toxine in this way 

 is very considerable : indeed of twenty parts only one part finds its 

 way into union with the nervous system. 



We now come to the important question of the significance of the 

 toxophile groups in organs. That these are in function specially 

 designed to seize on toxines 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 

 toxines, 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 investigator. It would indeed 

 be highly superfluous, for exam.ple, for all our native animals to possess 

 in their tissues atomic groups deliberately adapted to unite with abrin, 

 ricin, and crotin, substances coming from the 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 toxine. 



The first thought suggested by this assumption was that the atom 

 groups 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 proto- 

 plasm, and so are really assimilated, and those which have no such 

 capacity. To the first class Ijelong a portion of the food-stuff's far 

 excellence 3 to the second almost all our pharmacological agents, alkaloids, 

 antipyretics, antiseptics, &c. 



How is it possible to determine whether any given substance will 

 be assimilated in the body o<: 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 concerned enters into combination with 

 the protoplasm by a process of condensation involving loss of a portion 

 of its water. To take the example of sugar, in the union with proto- 

 plasm, not sugar itself as such but a portion of it comes into play, the 

 sugar losing in the union some part of its characteristic combining 

 reactions. The sugar behaves here as it does, e.g., in the gluco- 

 sides, from which it can only be obtained through the agency of 



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