HISTORIC DEVELOPMENT OF IMMUNOLOGY 31 



of vaccination against hay fever in this country, 

 and his work stimulated extensive study of this 

 form of active immunization which has now been 

 placed on a more complete basis by Koessler. 



All of these procedures were prophylactic, but 

 in 1904 Wright introduced active immunization 

 as a therapeutic measure in many chronic infec- 

 tions. He used, for the most part, cultures of 

 the specific microorganism killed by heat and, 

 when possible, prepared his vaccine from 

 strains isolated from the lesion to be treated. 

 Further, he made use of the opsonic index as a 

 means for determining the dosage of his bac- 

 terial vaccines. Largely owing to the advocacy 

 of Wright, killed cultures have acquired an im- 

 portant position in the treatment of almost all 

 infections which can be definitely associated 

 with a known type of microorganism. 



Serum Therapy Far more marked success 

 from a therapeutic point of view has been ob- 

 tained by passive immunization. The produc- 

 tion of antitoxic sera was made possible by the 

 discovery, by Roux and Yersin in 1889, that the 

 injury caused by infection with the diphtheria 

 bacillus was chiefly due to a soluble toxin which 

 the bacillus produced in culture as well as in the 



