SEROLOGY MANUFACTURE AND USE OF SERA AND VACCINES 271 



The sensitized bacterins differ from the ordinary bacterins in that they 

 are pre-charged or saturated with the specific amboceptors, thus when 

 injected hypodermically or intravenously, the body is at once stimulated 

 to form the specific antibodies (anti-endotoxins). They are prepared as 

 follows, using typhoid sero-bacterin as an example. Twenty-four hour 

 pure cultures of the Bacillus typhosus are placed in normal salt solution 

 (0.85 per cent.). The mixture is thoroughly emulsified and filtered into a 

 centrifuge tube and to it is added immune goat's serum (that is, blood 

 from a goat which has been immunized against typhoid) and let stand for 

 twenty-four hours at a temperature of 24 C., with frequent shaking. 

 Saline solution is added, shaken, and centrifuged for 5-6 minutes. The 

 supernatant liquid (saline solution containing most of the excess of im- 

 mune serum) is drawn off. More saline is added, shaken and again cen- 

 trifuged, and the supernatant liquid again drawn off (saline solution 

 containing the last trace of the excess of immune serum) . The reason why 

 the excess immune serum must be drawn off is because experience has 

 demonstrated that it would interfere with the development of the active 

 immunization by the bacterial antigen. The bacteria left in the cylinder 

 of the centrifuge are now said to be sensitized by the immune serum and 

 constitute the so-called sensitized bacterin or sero-bacterin, or in this par- 

 ticular case, the typho-serobacterin. Some bacteriologists are of the 

 opinion that the living sensitized bacteria should be used, whereas others 

 are of the opinion that the dead bacteria are just as effective and their 

 use is not accompanied by the possibility of spreading active infection, 

 although this is not likely as far as the typho-serobacterin is concerned. 

 (This organism developing in the intestinal tract and not hypodermically.) 

 It would appear that the present tendency is to prefer the killed bacteria. 

 For the purpose of killing the sensitized bacteria, heat or phenol, or other 

 antiseptic, is use. The bacteria are then counted by the Wright methods 

 (explained elsewhere) and standardized suspensions are made for use as 

 a preventive of typhoid and also as a cure. At the present time it is 

 customary to inject a trivalent typho-serobacterin, consisting of the sen- 

 sitized Bacillus typhosus and of Bacillus paratyphosus A and of B. para- 

 typhosus B. Definite numbers of the sensitized bacteria are injected at a 

 dose, from 125,000,000 to 2,000,000,000, suitably suspended in saline 

 solution. Most of the sensitized bacterins are used for the purpose^of 

 developing active immunizations rather than as cures, although some^of 

 them have-proven quite effective in certain chronic stages of disease. 

 The sero-bacterins possess the following properties and advantages over 

 the ordinary bacterins. 



i. They produce quick active and lasting immunity, which begins 

 within 24 to 48 hours after they are introduced into the system. 



