i 9 7 



effects of a more or less sharp specific attack, the physical 

 and mental condition of the individual may return to their 

 original state. Not always, however, is even the immunity 

 of the individual from modified, or even full-developed 

 secondary attacks, complete, as either may recur repeatedly, 

 so that it may be safely said that no heritable condition of 

 health is ever produced. 1 



Having thus far stated the case against heredity, I may now 

 be permitted to ask how is it, as frequently happens, that 

 these specific germs or poisons manifest such a selective 

 capacity that they may attack only one or two individuals in 

 a family, and leave the others unaffected ? How frequently 

 this happens is well known to every practitioner. While it 

 is quite true that a low physical condition induced by intem- 

 perance, bad feeding, chronic disease, over-crowding, want of 

 cleanliness, mental depression or fear, very often predisposes 

 individuals to succumb to an attack of some of the acute 

 infectious diseases, it must not be forgotten that there are 

 individuals in most families who, owing to some constitu- 

 tional peculiarities, are insusceptible of being influenced by 

 some of them, while yet other individuals are insusceptible 

 to the influence of other specific poisons. At the same 

 time it should be stated that insusceptible individuals may 

 sometimes act as media for the dissemination of some of the 

 exanthemata if allowed to pass from the sick room, and to 

 mingle with healthy persons. There is, in fact, not one of 

 these acute infectious diseases to which many individuals 

 are not more or less insusceptible ; and I contend that where 

 this insusceptibility has not been acquired by an attack of 

 some of the acute infectious fevers, it must have been 

 inherited as a constitutional peculiarity, although we cannot 

 1 Mr. Jonathan Hutchinson. 



