354 INFECTION AND RESISTANCE 



lary tip about one inch in length, having a capacity of about 0.05 

 c. c. graduated in 0.01 c. c. The bacterial suspension, after being fil- 

 tered through sterile cotton to remove fragments of the agar or other 

 foreign bodies, is centrifugalized in such a tube for half an hour at 

 about 2,800 revolutions a minute. The supernatant fluid and bac- 

 teria are removed down to the 0.5 c. c. mark and the sediment resus- 

 pended in 5 c. c. sterile salt solution by means of a capillary pipette 

 which gives a 1 per cent, suspension. 0.05 c. c. of streptococci sedi- 

 mented in this way represent quite constantly 16 mm. of dried bac- 

 terial substance. The number of organisms per cubic centimeter 

 contained in 1 per cent, suspension in this way are as follows : 



Streptococcus aureus and albus 10 billion 



Streptococcus 8 



Gone-coccus 8 " 



Pneumococcus (capsulated) 2.5 ' 



Bacillus typhosus 8 



Bacillus coli . . 4 " 



After the vaccines have been standardized suitable dilutions can 

 be made in salt solution to which 0.5 per cent, carbolic acid or some 

 other antiseptic has been added. The dilutions are usually so made 

 that from 100 to 500 million bacteria are contained in the cubic cen- 

 timeter, this being a suitable initial dose of most organisms. The 

 dilutions are placed in sterile bottles containing beads and fitted 

 with rubber caps. These bottles can be shaken 

 before use, the emulsion thoroughly distributed, 

 and the desired quantity can be taken out with a 

 sterile hypodermic syringe thrust through the 

 rubber cap after this has been covered with a 

 small amount of lysol or strong carbolic (see fig- 

 ure). After the dilutions have been made both 

 these and the stock vaccines should be sterilized. 

 Some workers sterilize always the stock vaccines 

 VACCINE STOCK and make the dilutions with aseptic proportions 



RUBBER TOP * n suc ^ a wa ^ ^ at no ^ urtner sterilization is 

 BOTTLE. necessary. This is preferable because the less 



heat that is applied the better it is for the 

 preservation of their antigenic properties sterilization is usually 

 accomplished by heat in the water bath. Wassermann's earlier 

 technique called for heating to 60 C. for one hour for a 

 number of consecutive days. It is generally considered at the 

 present time that it is better not to heat above 55 C. After the 

 vaccine has been heated its sterility must be controlled to aerobic 

 and anaerobic cultivation, and possibly by animal inoculation, al- 

 though, except in special cases, this is unnecessary. Some workers, 



