IMMUNITY. 183 



which it has met, but throws out more side chains than it can possi- 

 bly use. In other words, the over-stimulated cell secretes, as it were, 

 toxophil groups, and, as frequently happens in case of tissue stim- 

 ulation, the process continues to a point of over-compensation. 

 Finally the excess of toxophil groups thrown out by the cell be- 

 comes so great that many of them are cast off into the blood, lymph, 

 and other fluids of the body. These cast-off toxophil groups con- 

 stitute the antitoxin. Now if a toxin be introduced into the body 

 of an animal whose blood and lymph are filled with loose toxophil 

 groups, the toxin is neutralized by these detached side chains, and 

 the cell escapes injury altogether. In this way Ehrlich accounts for 

 the formation of antitoxins and the production of toxin immunity. 

 If the blood serum of an immunized animal be injected into a non- 

 immune animal and the latter be treated with the homologous toxin 

 the poison thus introduced combines with the antitoxin dissolved in 

 the body juices, and the cells of the animal thus treated wholly escape 

 any injurious effects. It may be well at this point to make the fol- 

 lowing quotation from Ehrlich's own statement on the subject : 

 " The theory above developed allows of an easy and natural explana- 

 tion of the origin of antitoxins. In keeping with what has already 

 been said, the first stage in the toxic action must be regarded as being 

 the union of the toxin by means of its haptophorous group to certain 

 side chains of the cell protoplasm. This union is, as animal experi- 

 ments with a great number of toxins show, a firm and enduring one. 

 The side chain involved, so long as the union lasts, cannot exercise 

 its normal nutritive physiological function — the taking up of definite 

 food-stuffs. It is, as it were, shut out from participating, in a 

 physiological sense, in the life of the cell. We are, therefore, now 

 concerned vrith a defect which, according to the principles so ably 

 worked out by Professor Carl Weigert, is repaired by regeneration. 

 These principles, in fact, constitute the leading conception in my 

 theory. If, after union has taken place, new quantities of toxin are 

 administered at suitable intervals and in suitable quantities, the side 

 chains which have been reproduced by the regenerative process are 

 taken up anew into union with the toxin, and so again the process 

 of regeneration gives rise to the formation of fresh side chains. In 

 the course of the progress of typical systemic immunization, as this 

 is practised in the case of diphtheria and tetanus toxin especially, 

 the cells become, so to say, educated or trained to reproduce the 

 necessary side chains in ever-increasing quantities. As Weigert has 

 confirmed by many examples, this, however, does not take place as a 

 simple replacement of the defect. The compensation proceeds far 

 beyond the necessary limit ; indeed, over-compensation is the rule. 

 Thus the lasting and ever-increasing regeneration must finally reach 

 a stage at which such an excess of side chains is produced that, to 

 use a trivial expression, the side chains are present in too great a 



