174 IMMUNE SERA 



wish to immunize against this toxin, to grow the 

 culture for the requisite length of time and under 

 the proper conditions for producing the toxin. 

 In the case of bacteria possessing certain endo- 

 toxins, it may be necessary to let the cultures 

 autolyze, so as to set these substances free, or the 

 bacteria may be crushed and ground for the same 

 purpose. On the other hand, we may wish to use 

 these bacteria for producing a specific agglutinat- 

 ing serum. In that case we often try to avoid 

 injecting these toxic substances. Our entire pro- 

 cedure might then have to be quite the reverse of 

 what has just been indicated. 



The Vaccines. Wright's method of preparing a 

 staphylococcus, typhoid, streptococcus, or gono- 

 coccus vaccine, is as follows: 



Several streak slant agar cultures are planted and 

 incubated for twenty to twenty-four hours. The 

 cultures are then washed off with normal salt solu- 

 tion, using from one to several cc. for each culture. 

 These suspensions are next heated to 55 C. in 

 order to kill the bacteria, and are then standard- 

 ized. By this is meant determining the number of 

 organisms per cc., for Wright always used definite 

 numbers of bacteria in his inoculations. This 

 standardization is readily accomplished by means 

 of the method devised by Wright, which is as fol- 

 lows : From a finger prick a drop of blood is sucked 

 up in a capillary tube to a mark made at any con- 



