IMMUNITY TO TOXINS I2Q 



of a given toxin might be reversed in the immunized leucocytes, 

 so that in place of being repelled, as under normal conditions, it 

 might be attracted. As far as phagocytosis depends on the 

 chemotactic attraction of leucocytes and the active suggestion of 

 organisms, we might expect it to be greatly increased if these 

 cells became immune. But there is no reason to see how a 

 similar increase need occur if it depends on a process akin to 

 agglutination, and resulting, perhaps, from a change in the surface 

 tension between the leucocyte and the organism. And that this is 

 the way in which the vast majority of the bacteria are taken up 

 in ordinary opsonin preparations appears probable. Active move- 

 ments of leucocytes are rarely seen in emulsions prepared for the 

 opsonic technique and examined in normal saline solution on the 

 warm stage. In other words, the opsonic index, though useful as 

 an index of certain activities of the serum, would appear not to 

 throw much, if any, light on the immunity of the leucocytes. 

 That must be sought by other means, notably by experiments in 

 vivo, and these lead us to the belief that the leucocytes may 

 become immune and may play a part of importance in acquired 

 immunity. 



But the facts which have been previously recorded concerning 

 the local reaction in animals which are being immunized to tetanus 

 toxin tend to support MetchnikofFs hypothesis, though the evi- 

 dence is somewhat indirect. We have already pointed out that 

 when normal horses are injected with small doses of this toxin 

 there is at first no local reaction, or but slight, and that as the 

 animal becomes more immune this local reaction becomes more 

 manifest a phenomenon which we have attributed to the 

 hypersensitiveness of the tissues. Now the local reaction is 

 inflammatory in nature, and the tumefaction which occurs is due 

 partly to oedema and partly to an access of leucocytes, so that it 

 would appear that in the production of immunity these cells 

 acquired the power of invading a tissue which is permeated with 

 toxin. If this is the case, we may assume that they have become 

 immunized to this toxin, and that they have changed in regard to 

 their chemotactic properties. This collection of leucocytes in 

 large numbers at the region of inoculation of toxins, where they 

 may form a sterile abscess of considerable extent, is a frequent 

 phenomenon in the production of diphtheria toxin ; and here, again, 

 it seems not improbable that the leucocytes have become, like the 

 tissue cells, more immune to the toxin. There are no inherent 



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