THE PROTECTIVE SUBSTANCES OF THE BLOOD. 375 



junctiva in man and animals. I have shown, furthermore, that it 

 is possible, by means of conjunctival instillations, to actively immu- 

 nize rabbits against abrin. Romer immunized a rabbit by means 

 of rapidly increased doses into the right eye and killed the animal 

 at the end of three weeks. It was then found that the conjunctiva 

 of the right eye which had been the site of the inflammatory process 

 was able, when ground up with a suitable amount of abrin, almost 

 completely to neutralize the action of this poison, whereas the other 

 conjunctiva, when similarly ground up with abrin, was unable to 

 protect the animal from death. From this Romer rightly concludes 

 that in this conjunctival immunization part of the antitoxin is fur- 

 nished by the conjunctiva which reacts locally. Aside from its 

 theoretical interest I believe that this demonstration of the local 

 origin of antitoxin at the site of injection possesses great practical 

 significance. In certain cases the possibility is thus given to trans- 

 fer part of the antitoxin production from the vital organs to the in- 

 different connective tissues. 



The third point concerns the thrusting-off of the surplus receptors. 

 A prerequisite for this thrusting-off is that the receptors in question, 

 which are normally firmly attached to the protoplasmal molecule, 

 become loosened. In several favorable cases it has been possible 

 to confirm this postulate of my theory experimentally, though to 

 be sure these deal with immunization by bacteria and not with solu- 

 ble poisons. Pfeiffer and Marx succeeded in showing that w r ith a 

 suitably conducted cholera immunization it is possible to find a 

 period at which the blood is still free from protective substances, 

 although the specific protective substances can be abstracted from 

 the blood-forming organs by crushing them up with salt solution. 

 In my opinion this can be due only to an extraction of receptors 

 which, since it is just previous to their extrusion, are only loosely 

 attached to the protoplasmal molecule. 



Almost simultaneously with Pfeiffer and Marx, the same results 

 were obtained by Wassermann with typhoid, and these were later 

 confirmed by Deutsch. In all of these experiments the hamato- 

 poetic system represents the site of production of these antibodies. 

 The significance of this circumstance for the immunizing process 

 has been pointed out by Metchnikoff's teachings. 



These few examples will suffice to show that the side-chain theory 

 has fully stood the test of experiment. During the many years of 

 my experimental activity I have not met a single fact which con- 



