208 A MANUAL OF BACTERIOLOGY 



organism in certain situations may be inaccessible to the blood- 

 stream and to the anti-serum, e.g. the vibrios in the bowel in 

 cholera. 



Another reason advanced is the extreme specificity of anti- 

 serum and the variability of bacteria so that many races or strains 

 of an organism may exist ; this has been proved in the cases of 

 the pneumococcus and the meningococcus. Hence the anti- 

 serum prepared with one race may not neutralise another race. 

 Attempts have been made to overcome this factor by preparing 

 the anti-serum by the injection of many races and so obtaining a 

 " polyvalent serum." 



The amboceptor or immune -body seems to link the 

 complement to the bacterium (Fig. 33) ; complement 

 remains free if the appropriate amboceptor be not present, 

 and bacteriolysis does not ensue. Bacteria first treated 

 with complement, i.e. fresh normal serum, washed with 

 saline by centrifuging, and then treated with the homo- 

 logous immune serum undergo no alteration ; but if the 

 process be reversed first treating with the immune serum, 

 washing, and afterwards treating with complement 

 bacteriolysis ensues. That is, the bacteria cannot directly 

 take up or fix complement, but they do take up ambo- 

 ceptor, and, having taken up amboceptor, they absorb 

 complement, both amboceptor and complement being 

 used up in the process. 



Complement is thermolabile, i.e. it is destroyed by 

 heating to 56 C. for thirty minutes ; while the ambo- 

 ceptor is thermostable, i.e. it is not destroyed by this 

 treatment. A serum containing complement is termed 

 an " active " serum ; one in which the complement has 

 been destroyed by heating to 56 C. is said to be " inacti- 

 vated." 



According to Ehrlich, fresh serum contains numerous 

 complements which are more or less specific for different 

 amboceptors (see also note, p. 216). When the comple- 

 ment is destroyed by heating it is converted into " com- 



