126 TISSUE IMMUNITY TO TOXINS 



these latter should continue to live after the receptors had been 

 lost. But this seems based on a misconception of Ehrlich's 

 theories of cell-nutrition. We must imagine each molecule to be 

 provided with a very large number of varieties of side-chain, each 

 adapted to the seizure of a different form of food-molecule, so 

 that the complete loss of one variety does not imply that the cell 

 will suffer in nutrition. The only result is that more work will 

 be thrown on the receptors that remain. There is nothing im- 

 probable in this. It is in the highest degree likely that so 

 important a function as nutrition should not be dependent on the 

 functional integrity of every part of the molecule. The occurrence 

 of tissue immunity from loss of receptors is at least possible. 



An alternative theory asserts that the cells of the body retain 

 their power of combining with toxin, but lose their susceptibility 

 to the action of the toxophore group of the latter, at the same time 

 losing their power of producing antitoxin. We may explain the 

 latter phenomenon by saying that the receptors in question 

 become sessile and incapable of being shed. There is experi- 

 mental evidence that some receptors are naturally of this nature, 

 and it is quite possible that ordinary deciduous receptors might 

 change in this way. As we shall see, tissue immunity in which 

 the toxin becomes anchored to the cell, but without injuring it or 

 stimulating it to produce antitoxin, is met with in some forms of 

 natural immunity, and it is quite possible that it may occur in the 

 process of hyperimmunization by vaccines, though direct proof is 

 lacking. Another process of somewhat similar nature may occur, 

 which has also its analogue in natural immunity. Thus when 

 animals are immunized to tetanus they still retain their suscepti- 

 bility to that toxin if the injection be made directly into the 

 brain. It is obvious, therefore, that the cells of the central 

 nervous system are still susceptible. W 7 hy, then, do the animals 

 not develop tetanus if the injections be made subcutaneously ? 

 We exclude, of course, the case in which antitoxin is present in 

 the blood and the leucocytes are functionally active. It will be 

 shown subsequently that some forms of natural immunity depend 

 upon the fact that some cells in the body unite with the toxin, and 

 have, indeed, a great affinity for it, but are not injured thereby, 

 whereas others have an affinity for it, but are killed by its action. 

 Obviously, if the toxin be injected into tissues of the former class 

 it will be absorbed, none will reach the susceptible second class of 

 cells, and no toxic symptoms will result. Now let us suppose 



