130 Immunity 



were specific, and that when a culture of one kind of bacteria 

 was injected into an animal, the immediate effect was to 

 diminish the activity of the serum for that species, though 

 not necessarily for other species. The diminution of bac- 

 tericidal energy was shown by him to depend upon the 

 presence of the bacteria, as the injection of filtrates of bac- 

 terial cultures did not affect the bactericidal properties of 

 the serum. This was a very important observation. 



There is a correspondence between the behavior of the 

 phagocytes and the body juices. When the activity of the 

 phagocytes toward the bacteria is increased, the bactericidal 

 activity of the serum is usually intensified. But immunity 

 is only partly explained by alexins and bacteriolysis, for 

 it embraces the ability of the organism to endure the effects 

 of toxins some of which are in no way connected with 

 bacteria. 



Tolerance to certain toxins is, of course, natural to many 

 animals, and tolerance to usually destructive toxins natural 

 to a few. This toxin-neutralizing or annulling factor 

 cannot be identical with the bacteria-destroying mechanism. 

 Cobbett,* Roux and Martin, f and BoltonJ have shown that 

 horses that cannot be supposed ever to have come into 

 contact with diphtheria bacilli, vary considerably in their 

 resistance to diphtheria toxin, and that the serum of the 

 resisting horses contains something that destroys or neu- 

 tralizes the toxin in vitro, as well as exerts a protective 

 influence upon animals into which it is injected. This 

 substance exerts no inimical action upon the diphtheria 

 bacilli, beyond what a normal serum would do, therefore 

 cannot be alexin, but must be antitoxin. Abel found 

 that the blood of healthy men occasionally contained some 

 substance capable of neutralizing diphtheria toxin; Stern 

 found one normal serum capable of protecting against typhoid 

 infection and Metschnikoff one that protected against cholera 

 infection. Fischel and Wunschheim|| found newly born 

 babies immune against diphtheria, presumably because of 

 the presence of a small quantity of demonstrable protective 

 substance in the blood. These are, however, peculiar and 

 exceptional cases. 



* "Lancet," Aug. 5, 1899, n, p. 532. 



t "Ann. de 1'Inst. Pasteur," vin, p. 615, 1894. 



t "Jour, of Experimental Medicine," July, 1896, I, No. 5. 



"Centralbl. f. Bakt.," etc., xvn, pp. 36, 1895. 



|| "Zeitschr. fur Heilkunde," 1895, xvi, p. 429-482. 



