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that they are essentially identical in structure ; the only 

 change is in the vigour of their life, developed hereditarily. 

 What is vigour, what is life, what is heredity ? When we 

 turn now to the animals in whom the zymotic diseases do 

 not recur, and to the phenomena of protective vaccination, 

 may we not assume that some educational influence of the 

 same kind is exerted upon the living cells of the animal 

 body ? The microbe which kills the unvaccinated animal 

 is the same, in all respects, as the microbe which fails to kill 

 the vaccinated animal ; the difference is in the cells of the 

 animal attacked. When it is suggested, as in the case of 

 small-pox for instance, that the vaccination has used up 

 some material, only rarely elaborated, in the body, and 

 necessary for the development of the microbe, are we not guilty 

 of as crude an attempt to represent the fact, as was the old 

 notion of a material caloric ? May we not with more philo- 

 sophy regard the phenomenon as some mysterious educational 

 influence, in the one case, as well as in the other. Regard- 

 ing the contest between the microbe and the living cells of 

 the body as a struggle for existence, may we not assume 

 that resisting vigour is developed in the one, as attacking 

 vigour is developed in the other ? Miquel records a most 

 remarkable instance which he says " seemed to show that 

 bacteria are endowed with instinctive movements." A 

 bacillus making a circular movement was arrested by a mass 

 of germs. It vigorously attacked the mass and by rapid 

 backward and forward pushes, attacking now right, and 

 now left, cleared a cul-de-sac, which it finally developed 

 into a complete canal; then it appeared to rest from its efforts. 

 Miquel was utterly astonished by the "address" with which 

 the bacillus thus disengaged itself from the vicious circle in 

 which it found itself engaged. Is there anything more 

 wonderful in this, than in the apparently instinctive move- 

 ments observed by Darwin in the tips of the radicles of 

 plants, the apparently muscular memory to which Romanes 



