HEMOLYTIC SERA AND THEIR ANTITOXINS. 209 



3. Heated cholera serum recovers its original bactericidal energy 

 on tke addition of a normal serum that is itself only faintly bac- 

 tericidal. A small amount of intact or of heated cholera serum 

 suffices to confer an intense specific bactericidal power on a con- 

 siderable amount of normal serum. This power is evidenced by a 

 granular transformation in the added vibrios.* 



4. Normal serum alone frequently causes a granular transfor- 

 mation of vibrios to a less degree, particularly if the vibrios are 

 attenuated. 



5. Normal serum heated to 55 degrees loses the property of 

 restoring the bactericidal activity to heated cholera serum. 



Our theory founded on these facts is comprised in the two follow- 

 ing propositions: 



A. The bactericidal property of cholera serum, or of analogous 

 sera, is due to the presence of two distinct substances: the first, 

 which may be called preventive substance or antibody (later called 

 sensitizer), is characteristic of immune serum, is specific and resists 

 a temperature of 55 to 60 degrees and even more. The other, or 

 proper bactericidal substance, the alexin, occurs in the serum of 

 normal as well as of vaccinated animals, and is destroyed on heating 

 to 55 degrees. Heating cholera serum to 55 degrees does not 

 destroy the preventive substance, but simply eliminates the alexin. 

 As this alexin is present in normal serum the addition of such serum 

 restores to heated cholera serum its original activity.! 



In such a mixture cholera serum again contains both substances 

 originally present, the collaboration of which is essential in pro- 

 ducing intense specific bacteriolysis. 



The preventive substance, in other words, heated cholera serum, 

 is not at all bactericidal. Normal serum on account of its alexin 



* We advocated such a mixture in vitro as a practical diagnostic method for the 

 cholera vibrio. 



f We have been surprised to find that certain authors, particularly in Germany, 

 give a very inexact historical account of these ideas, frequently attributing the 

 first consideration of these facts to authors who have only recently considered the 

 question. Consequently we may be permitted to refer to certain passages in our 

 memoir of 1895. See, for example, on p. 58, and on p. 59. 



We shall later quote other references in the text, particularly when we come 

 to consider the unity of the bactericidal substance in different immune sera, 

 and the occurrence of bactericidal power in the fluids of passively immunized 

 animals. 



