IMMUNITY 297 



serum of another artificially immunised organism ; and even 

 by ingesting the microbes or their products. (See A. A. Kan- 

 thack, Allbutt's System of Medicine, vol. i., article " Infection.") 



It seems that artificial immunity depends on processes within 

 the body which make the tissues able to destroy intruding 

 bacteria and to rob their products of their fatal potency. It 

 seems that specific anti- toxins are formed which immunise 

 the body to specific infection. 



An acquired specific immunity may be transferred from 

 a mother to her offspring through the placenta, but this is 

 not in the strict sense inheritance. Ehrlich and others have 

 shown experimentally that rabbits and the like may be born 

 immune if the mother has been artificially rendered immune ; 

 and it has been asserted that in mankind the foetus may 

 become, through the mother, immune to smallpox. 



In support of the view that those who are infected with a 

 plague and survive can transmit relative immunity to their 

 offspring, attention is called to the fact that epidemics have 

 their day and cease to be. But this admits of another inter- 

 pretation — the plague eliminates the most susceptible and 

 leaves the race in this way more resistent. What is transmitted 

 is the inborn power of resistance — which may be enhanced by 

 the selective process, especially if the plague is very severe 

 and lasts a long time. It is to be feared that there is very little 

 evidence of the transmission of acquired immunity — to smallpox, 

 for instance ! 



What is to be made of the alleged fact that two of the commonest 

 infective diseases in Britain— namely, scarlet fever and measles- 

 are much less virulent than they used to be ? According to a 

 skilful pathologist, Dr. William Russell, " this is almost certainly 

 to be attributed, not to an attenuation of the virus, or to im- 

 proved treatment, but to a measure of immunity acquired by a 

 population whose progenitors for generations have passed 

 through the ordeal of these infections." 



