184 BACTERICIDAL OH ANTI-BACTERIAL IMMUNITY. 



this inert serum a little fresh blood serum from a normal guinea-pig, 

 which is not in itself lytic (see p. 182) the original dissolving power of 

 the heated serum for rabbit corpuscles was at once restored. The infer- 

 ence from this experiment is obvious. The dissolving capacity of this 

 artificially lytic serum is due to two distinct substances. One of these, 

 that one which results from the adaptation of the animal to the alien 

 blood, is stable at 56 C. ; the other, which is present in normal serum, is 

 rendered inert at 56 C. ; that is, it is very labile. These two substances 

 were named early and have been often renamed. For the present we 

 may speak of the stable substance resulting from the adaptation to the 

 alien blood as the immune substance or immune body, and of the other, 

 more sensitive to heat and present in normal serum, as alexin, a name 

 which was long ago applied by Buchuer to a substance or substances in 

 normal serum, to which its germicidal capacity, first clearly demonstrated 

 by Xuttall, was attributed. 



There now followed a series of important studies by Ehrlich and his 

 associates which throw still further light upon these curious lytic agents. 



We have seen that in order to secure the immune substance free from 

 the alexin one has only to heat the lytic serum to 56 C., for half an 

 hour, when the alexiu is destroyed. If one wishes to secure the alexiii 

 apart from the immune substance he makes use of a very curious prop- 

 erty of the latter; namely, its capacity of uniting with the cellular ele- 

 ment under whose influence it was elaborated. For example, if one 

 places a small portion of the serum of a rabbit which has been adapted 

 to beef blood in contact with beef corpuscles at a low temperature ' for a 

 few hours, he will find that the immune substance has formed so stable 

 a combination with the corpuscles that on their separation from the fluid 

 by centrifugation, none of the immune substance, but all of the alexin, 

 will be left in the fluid. 



That the corpuscles under these conditions actually contain the im- 

 mune substance is readily shown by adding to them a little normal serum 

 containing alexiu but no immune substance whereupon the lysis will 

 at once take place, as shown by the red color of the fluid. This union of 

 the immune substance with corpuscles is specific, occurring only with the 

 corpuscles of the animal species used in the adaptation. 



Many other points of extreme interest and significance have been re- 

 vealed in these studies on artificial haemolysis which the scope of this 

 book does not permit us to touch upon. 



The question of a multiplicity of immune substances and of alexins 

 has been brought forward, and it seems probable, especially from the 

 researches of Ehrlich, that in adaptation of each animal species to a 

 single form of cell several immune bodies may be developed. It is not 

 unlikely, furthermore, that more than one alexin may be normally pres- 

 ent in the blood serum of each animal species, and that a single immune 

 body may be capable of uniting with several forms of alexin. 



1 It is necessary to reduce the temperature in this experiment in order to inhibit the 

 action of the lytic agencies. 



