SIDE-CHAIN THEORY 89 



the needed complement. The amboceptor, from this point 

 of view, has a double specific combining power on the one 

 hand with the erythrocyte and on the other with the com- 

 plement. 



Generally, the serum of any animal is more or less hemolytic 

 with respect to the corpuscles of an animal of another species, 

 but in some normal sera this power is very prominent. This 

 is the case in eel's serum. Here too the hemolysis is due to 

 the interaction of two bodies. The strongest evidence against 

 Bordet's conception of a sensitizing substance and in favor 

 of the side-chain theory is that resulting from the study of 

 cobra venom. Regarded as a hemolytic agent, cobra venom 

 contains amboceptors only. If it be mixed with thoroughly 

 washed goat erythrocytes, which contain no endocomplement, 

 no hemolysis results until some complement (normal serum) 

 be added also. If, however, snake venom and complement be 

 mixed together so that there is a large excess of amboceptors 

 in the mixture and then added to blood, then the erythrocytes 

 will not undergo hemolysis. This is due to the deviation of the 

 complement) all the complement available for the activation 

 of the erythrocyte-amboceptor compound having become 

 united with those amboceptors which are floating free and 

 are not anchored to the erythrocytes. Such a result cannot 

 be explained on Bordet's theory. Furthermore, in the case of 

 snake venom it has been found that the complement which 

 unites with the venom amboceptor is the well-known simple 

 substance lecithin. If a chloroform solution of lecithin be 

 shaken for two hours with cobra venom, a chemical compound, 

 cobra lecithin, is formed which is actively hemolytic toward 

 ox erythrocytes. 



Side-chain Theory. The theory which has won greater 

 acceptance than Bordet's is the side-chain theory of Ehrlich 

 and Morgenroth. It is most easily understood by considering 

 the simplest case, that of antitoxin formation. If a bouillon 

 culture of diphtheria bacillus be filtered through a Pasteur- 

 Chamberland filter, the filtrate will contain diphtheria toxin, 

 and will, if injected into susceptible animals, cause death. 

 If, however, the toxin be injected at intervals of a few days 

 apart, at first in sub-lethal doses, the animal will become immune. 

 The serum of such an immune animal, if injected into a normal 



