424 



Dr. Paul Ehrlich. 



Croonian Lecture.—" On Immunity witli Special Reference to 

 Cell Life." By Professor Dr. Paul Ehrlich, Director of the 

 Eoyal Prussian Institute of Experimental Therapeutics, 

 Erankfort-on-the-Maine. Eeceived March 17, — Eeacl March 

 22, 1900. 



[Plates 6 and 7.] 

 (Translation.) 



Honomed President, my lords and gentlemen, — It is to me the very 

 greatest honour that I have been summoned here by your most highly 

 esteemed Society, which for more than two centuries has represented 

 and still represents the centre of the scientific life of England, in 

 order that I may deliver the Croonian Lecture. I consider I am not so 

 much personally concerned in the honour that you bestow on me, and 

 that I shall not err if I see in it a recognition of the scientific path 

 which I, in company with many others, have sought to follow, and 

 which in your eyes suffices to place the field in which I work on a 

 footing alongside of exact science. It is an extreme pleasure for me 

 to have the privilege of addressing so many medical colleagues vnth 

 whom for so many years I have been bound in close ties of friendship, 

 and who have always been the first to welcome and to give recognition 

 to the results of my work. 



Since Jenner made his great discovery of the protective action of 

 vaccinia against small-pox, a century has passed away. During these 

 years that terrible scourge of mankind has been almost completely 

 eradicated from the civilised world. The beneficial consequences of 

 Jenner's discovery are so evident to all who have any wish to properly 

 appreciate them, that one wonders why, during so great a portion of 

 the long period of 100 years, they were allowed to stand alone, with- 

 out any endeavour being made to induce an artificial immunity in 

 the case of other infectious diseases. This is all the more remarkable 

 because Jenner's discovery demonstrated in their entirety those essential 

 principles which, in later times, have been established for other infec- 

 tious diseases. 



In the first place, it was shown that by the use of an attenuated 

 virus, which of itself was non-injurious to the organism, it was 

 possible to ward off the disease caused by the virulent virus. 

 Jenner also established — what is most important from the practical 

 point of view — that by the inoculation of the weakened poison 

 there was produced not only an immediate, but also an enduring, 

 protection. That Jenner's discovery remained so isolated was due 

 essentially to the fact that the theoretical conceptions of the cause 

 and nature of infectious diseases made no advance during the sub- 

 sequent decades ; indeed, it would be an interesting topic for some 

 historian of medicine to trace step by step the gradual advance in the 



