28 



VACCINE AND SERUM THERAPY. 



of microorganisms are taken from a stock culture. Usually liv- 

 ing freshly grown bacteria are used to make emulsions. The 

 principle, or practically only exception to this has been in the 

 determination of the opsonic index for the bacillus of tubercu- 

 losis, for which often killed and old cultures of the organism have 

 been used to make the bacterial emulsion. 



In all cases it is intended that the bacteria shall be well sep- 

 arated and suspended uniformly in salt solution. The tech- 

 nique for making the bacterial suspension varies with the differ- 

 ent organisms, some of which it will be necessary to consider 

 separately. The organisms for which the opsonic index is de- 

 termined may be divided into three classes. 



A. Many of the organisms belonging to this 

 class grow on the ordinary media, while for 

 others, media containing blood or other body 

 fluids are necessary. The organisms occur 

 singly or in pairs and when present in larger 

 groups the cell aggregates can be easily 

 broken up. 



(a). Mic. pyogenes aureus, albus and citreus, 

 B. coli, B. typhosus, B. pyocyaneus, etc., are 

 grown on slant agar for twenty-four hours 

 at 37 C. Various investigators, including 

 Wright, have used four to five hour cultures 

 of these organisms. 



(b). Mic. gonorrhoeas has usually been 

 grown on hydrocele or human blood agar. 

 Cole and Meakins obtained their cultures from 

 growth on agar in which 0.5 c.c. of fresh 

 blood had been added to 10 c.c. of ordinary 

 agar. The age of the cultures used has varied 

 from four to twenty-four hours incubation 

 at 37 C. 



(c). Mic. meninigitidis, Mic. pneumonias, 

 etc., produce good growth on sheep serum 

 agar. The cultures have usually been incubated at 37 C. from 

 twelve to twenty-four hours. 



To each culture of the proper age about ten drops of sterile 

 normal salt solution are added. With a platinum loop the cul- 



FIG. 7. 



