ACQUIRED IMMUNITY 61 



No lasting immunity is conferred by one attack in: 



Infection with the Pyogenic cocci 

 Gonorrhea 

 Pneumonia 

 Influenza 

 Glanders 

 Dengue fever 



Diphtheria in general protection, second attack in 0.9 

 per cent, cases-0.01 antitoxin unit per c. c. of circu- 

 lating blood protects. 

 Recurrent fever 

 Tetanus 

 Erysipelas 

 Beri beri 

 Tuberculosis 



There is another group of diseases in which the imnmnological 

 conditions after infection are as yet not clear namely, protozoan 

 infections like malaria and trypanosomiasis, and treponema diseases 

 like syphilis. In these conditions reinfection seems to be impossible 

 only so long as the individual still harbors the microorganism, but no 

 lasting immunity is conferred. We have discussed these conditions 

 in extenso in the section on syphilis immunity, (see p. 508). 



These observations actually form the point of departure of that 

 entire branch of medical science which devotes itself to the study of 

 resistance to infection, serum diagnosis, and specific therapy, and 

 it will be seen that all the facts that have been gathered upon these 

 subjects are the fruits of detailed analysis of this phenomenon of 

 acquired immunity. 



Its occurrence in many instances nas been so striking that ancient 

 observers, long before the birth of rational medicine, referred to it, 

 and often drew from it conclusions of great hygienic importance. 

 Thucydides, in the second book of his account of the Peloponnesian 

 Wars, in describing the plague at Athens, notes the apparent safety 

 from reinfection of those who had recovered, suggesting the possibil- 

 ity of their being therefrom immune against disease in general. The 

 literature of the Middle Ages and of earlier modern times contains 

 numerous further references which indicate that acquired resistance 

 was clinically recognized as a result of recovery from many diseases. 

 The phenomenon was not only observed, but put to practical utiliza- 

 tion by the ancients of China and India. Thus the practice of inocu- 

 lating children with small-pox material from the active pustules of 

 patients, or making them sleep in beds or wear the shirts of sufferers 

 was a dangerous practice but logical, on the reasoning that the disease 

 conveyed to a person in full health and good condition would probably 

 take a mild course and confer immunity, while the naturally acquired 

 disease, contracted often because of the weak and debilitated condi- 

 tion of the individual, would be more apt to end fatally. 



