248 BACTERIA IN INFECTIOUS DISEASES. 



likely to reveal to us the complicated molecular struc- 

 ture of the protoplasm upon which, possibly, the proper- 

 ties under consideration depend, it will be best, for the 

 present, to limit ourselves to a consideration of the living 

 cells of the body. These cells are the direct descend- 

 ants of pre-existing cells, and may all be traced back to 

 the sperm-cell and germ-cell of the parents. Now, the 

 view which I am endeavoring to elucidate is, that dur- 

 ing a non-fatal attack of one of the specific diseases, the 

 cellular elements implicated, which do not succumb to 

 the destructive influence of the poison, acquire a tol- 

 erance to this poison which is transmissible to their 

 progeny, and which is the reason of the exemption 

 which the individual enjoys from future attacks of the 

 same disease. 



4 ' The known facts in regard to the hereditary trans- 

 mission, by cells, of acquired properties, make it easy to 

 believe in the transmission of such a tolerance as we 

 imagine to be acquired during the attack ; and if it is 

 shown by analogy that there is nothing improbable in 

 the hypothesis that such a tolerance is acquired, we shall 

 have a rational explanation, not of heredity and the 

 mysterious properties of protoplasm, but of the partic- 

 ular result under consideration. The transmission of 

 acquired properties is shown in the budding and graft- 

 ing of choice fruits and flowers, produced by cultiva- 

 tion, upon the wild stock from which they originated. 

 The acquired properties are transmitted indefinitely ; 

 and the same sap which on one twig nourishes a sour 

 crab-apple, on another one of the same branch is elab- 

 orated into a delicious pippin. . . 



" The tolerance to narcotics opium and tobacco, 

 and to corrosive poisons arsenic, w r hich results from a 

 gradual increase of dose, may be cited as an example of 

 acquired tolerance by living protoplasm to poisons, 



