MICROBES— INFECTION— IMMUNITY 459 



no appropriate receptors for the haptophore group of the 

 toxm molecule, and where these are absent no attack on 

 the cell protoplasm is possible. 



B. Anti-hacterial Ser 



um. 



Immunity may be produced by the injection of Anti- 

 hacterial Serum which is obtained by hyper- immunising an 

 animal with bacteria ; by this means the blood serum 

 acquires properties which when injected will protect 

 another animal from a poisonous dose of bacteria. Such a 

 serum is described as preventive, and it can be studied 

 outside the body, for on the addition of such serum to the 

 microbes the latter may be destroyed. 



No such destruction takes place, if prior to the addition 

 of the serum to the microbe it be heated to a temperature 

 of 55° C. ; but the destroying action can be reproduced by 

 adding to it the fresh serum of an animal of the same 

 species which has not been immunised. From this it 

 follows that to produce the destructive effect two substances 

 are necessary, one stable which is not destroyed and one 

 unstable which is destroyed by heating to 55° C. The 

 stable substance is called, 



By Ehrlich the ' Amboceptor.' 



By Bordet the ' Substance scnsibilisatrice.' 



By Metchnikoff the 'fxateur.' 



The unstable substance is called. 



By Ehrlich the ' complement.' 



By Bordet the ' alexin.' 



By Metchnikoff the ' cytasis.' 



Ehrlich explains the destructive action of this serum on 

 bacteria by his lateral chain theory : he assumes that 

 under the repeated injection of bacteria the body cell casts 

 off a ' receptor ' which is composed of two groups : 



1. A cytophile group. 



2. A complementophile group. 



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