OPSONINS AND PHAGOCYTOSIS 173 



uation or weakening or decrease of virulence is accomplished in 

 several ways: in some cases by growing at high temperatures, as 

 for anthrax, heating to temperatures just below the thermal 

 death-point, as in blackleg, by animal passage, as in small-pox, or 

 by growth on artificial media, as with members of the hemorrhagic 

 septicemia group. 



Vaccines consisting of dead organisms are called bacterins. 

 These are prepared and sold commercially under various trade 

 names. They usually consist of pyogenic organisms which have 

 been killed by heat. The injection of these bacterins has been 

 shown to increase the opsonic index for specific organisms when 

 properly administered. It has been found, however, that there are 

 many strains of some of the pyogenic bacterial species, for example, 

 of Streptococcus pyogenes, and that vaccination against one strain 

 does not always protect against another. Vaccines are, therefore, 

 prepared containing organisms isolated from as many sources 

 as possible and containing many races or strains. Such a vaccine 

 is called polyvalent, a vaccine containing but one strain, univa- 

 lent. 



Autogenic Vaccines. Inasmuch as it cannot be readily deter- 

 mined to what strain a particular organism causing a chronic 

 bacterial infection, such as suppuration in a fistula, belongs, it is 

 sometimes desirable to prepare a vaccine of this particular organ- 

 ism for this single case. A vaccine prepared in this manner, to be 

 used in the animal from which the organism was isolated, is said 

 to be autogenic. The use of autogenic vaccines, carefully prepared 

 and standardized, has proved successful in many cases in the treat- 

 ment of stubborn and chronic suppurative conditions. The tech- 

 nic of preparation and use follows. 



Isolation of Organism. In many instances a slant agar culture, 

 made directly by securing material on a sterile platinum loop 

 from the deeper parts of the wound or abscess, will prove to contain 

 only the causal organism. In most cases, however, it will be found 

 advisable to plate directly in agar and incubate at blood-heat. 

 An examination of the colonies will reveal the causal organism 

 (or organisms in a mixed infection). 



Preparation of Vaccine (McCampbell). Into each of two flat 

 flasks or bottles, 100 c.c. of nutrient agar is placed, sterilized, and 



