H^EMOLYTIC AND OTHER SERA 479 



control is got by substituting in another experiment the same 

 amount of heated normal serum for the anti-serum. If there is 

 free complement left there will be corresponding lysis of the red 

 corpuscles ; if the complement has all been fixed there will be no 

 lysis. To take an example from Muir's experiments, it was found 

 that an emulsion of the bacteria alone took up '03 c.c. of guinea- 

 pig's complement, whilst the same amount of bacteria treated 

 with immune-body took up '13 c.c. The all-important action of 

 the immune-body is thus to bring an increased amount of com- 

 plement into union with bacteria ; whether death of the bacteria 

 will result or not will depend ultimately on their sensitiveness 

 to the action of the particular complement. 



It is to be noted that with a bactericidal serum there is 

 an optimum amount of immune-body which gives the greatest 

 bactericidal effect. If this amount be exceeded the bactericidal 

 action becomes diminished and may be practically annulled. 

 This result, which is generally known as the Neisser-Wechsberg 

 phenomenon, has been the subject of much controversy, and 

 cannot yet be said to be satisfactorily explained. It would 

 accordingly be out of place to discuss here the different views 

 with regard to it. (Regarding some theoretical considerations 

 as to the therapeutic applications of antibacterial sera, vide 

 p. 489.) 



The laws of lysogenesis are, however, not peculiar to the 

 case of solution of bacteria by the fluids of the body, but, as has 

 been shown within the last few years, hold also in the case of 

 other organised substances, red corpuscles, leucocytes, etc., when 

 these are introduced into the tissues of an animal as in a process 

 of immunisation. Of such sera the hsemolytic have been most 

 fully studied, and owing to the delicacy of the reaction and the 

 ease with which it can be observed, have been the means of 

 throwing much light on the process of lysogenesis, and thus on 

 one part of the subject of immunity. A short account of their 

 properties may now be given. 



Hcemolytic and other Sera. It has been known for some time 

 that in some instances the blood serum of one animal has, in 

 certain degree, the power of dissolving the red corpuscles of 

 another animal of different species ; in other instances, how- 

 ever, this property cannot be detected. Bordet showed that 

 if one animal were treated with repeated injections of the 

 corpuscles of another of different species, the serum of the former 

 acquired a marked hsemolytic property towards the corpuscles of 

 the latter, the property being demonstrated when the serum is 

 added to the corpuscles. Bordet also found that the haemolytic 



