A SECOND ATTACK. 



229 



poison for weeks, and was inoculated with it, but 

 never took the disease. Whether this animal had had 

 a mild attack before, or whether her escape was due 

 to some other circumstance, was not determined. But 

 ought we not to work to find out how to induce such 

 a disease mildly in other animals ? Will the public 

 neither supply us with the means to discover, on con- 

 dition that if the discovery be made it be given freely 

 to the world, nor offer a reward sufficiently large to 

 encourage an observer to risk all he has, and spend 

 many years in the prosecution of what may turn out 

 to be an absolutely barren investigation ? Many a 

 scientific man would work for the best years of his 

 life for the value of one monster gun, and many 

 valuable investigations might be conducted for a sum 

 equal to that spent upon a single discharge. 



In cases where "protection" has been obtained, 

 the change effected in the organism, it may be re- 

 marked, is general and complete. The entire mass 

 of the blood is in some way altered, and there is not 

 the smallest particle of the body which is not efficiently 

 " protected " against invasion by certain special 

 disease germs. The result may be explained by 

 supposing that changes have occurred in the blood 

 only, without any alterations having been necessarily 

 effected in the solid tissues. All contagious fevers 

 are, in fact, essentially blood diseases, so that in dis- 

 cussing the nature of the changes which may be 

 instrumental in effecting " protection/' we may con- 



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