482 IMMUNITY. 



specially developed during the process of immunisation, and gives 

 the anti-serum its special character ; it is usually known as the 

 immune-body (Ehrlich) or substance sensibilisatrice (Bordet). 

 It is comparatively resistant to heat, and can usually be subjected 

 to 65 C. for an hour without being destroyed. It is apparently 

 the protective substance, as an anti-serum does not lose its pro- 

 tective power when heated to the temperature mentioned. It, 

 however, cannot produce bacteriolysis alone, but requires for this 

 another substance present in normal serum. This latter is more 

 labile, being readily destroyed at 65 C., and even by half an 

 hour at 55 C. ; it is known by various names addiment or 

 complement (Ehrlich), alexine or cytase (French writers). We 

 shall speak of the two substances just described as "immune- 

 body" and ''complement" respectively. 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 haemolytic have been most fully studied, and have 

 been the means of throwing much light on the process of lyso- 

 genesis, 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, the serum of the former acquired a 

 marked haemolytic property towards the corpuscles of the latter, 

 the property being demonstrated when the serum is added to 

 the corpuscles. A mixture of five parts of defibrinated blood, 

 which of course contains the corpuscles, and ninety-five parts 

 of .75 per cent chloride of sodium solution is used, and to 

 this varying quantities of the haemolytic serum are added and 

 allowed to stand for some time at a warm temperature, usually 

 for one hour at 37 C. Bordet also found that the haemolytic 

 property disappeared when the haemolytic serum was heated 

 at 55 C., but was regained on the subsequent addition of 



