THE PRESENT EVOLUTION OF MAN— PHYSICAL 225 



attenuated when subjected to a temperature of from 

 42° to 43° C. 



But in diseases in which the incubation period is 

 short, and in which the microbes pervade the whole 

 body, any attempt to produce immunity by inoculation 

 with a weaker virus, aftar the host has been infected 

 by the stronger virus of the normal disease, must 

 necessarily be vain. In such a case the phagocytes, 

 paralyzed or destroyed by the stronger toxins, are unable 

 to react in response to the stimulation from the weaker 

 toxins, and death ensues ; or if death does not ensue it 

 is because the phagocytes have been able to react from 

 a position of no acquired advantage to the stimulation 

 of the strong toxins. So skin-ceUs in the presence of 

 great heat disregard and do not react to the stimulation 

 of lesser heat (which then but adds to the effect of 

 the other), or if they do react at all and are not 

 destroyed, react in response to the stimulation of the 

 greater heat. So other kinds of cells in the presence 

 of large doses of opium, tobacco, alcohol, &c. (toxins 

 in fact) disregard the action of smaller doses given 

 shortly after (which indeed but supplement the action 

 of the greater doses), and perish, or if they do not 

 perish, but react, react to the stimulation of the stronger 

 doses. Therefore in such a disease as small-pox, in 

 which the toxins are rapidly produced, and in which 

 the microbes pervade the whole body, protective inocu- 

 lation after infection is useless. To be effectual it 

 must be made at a time antecedent to infection, which 

 is what is done in vaccination against small-pox; at 

 the least if made after infection it must be made at a 

 time antecedent to the appearance of symptoms of 

 illness — i. e. during the incubation period, before the 

 virulent toxins have been elaborated, — and then it will 

 be successful only if the attenuated microbes elaborate 



Q 



