Antitoxin in Natural Immunity 107 



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 that of the body juices in animals with 

 acquired immunity, in that the activity of the phagocytes 

 toward the bacteria is increased, and the bactericidal activ- 

 ity of the serum intensified. The experiments of Pfeiffer, 

 Pfeiffer and Kolle, and of Bordet upon the bacteriolysis 

 taking place through factors brought out by experimental 

 immunization have already been mentioned. But immunity 

 is only partly explained by alexins, for in acquired immunity 

 we commonly encounter an increased tolerance to bacterio- 

 toxins and other toxins not in any way connected with 

 bacteriolysis and evidently depending upon other defenses. 



The tolerance to certain toxins is, of course, natural to 

 many animals. There are also exceptional cases of natural 

 immunity against toxins, however, that call our attention to 

 certain new factors that become very important for consid- 

 eration at this point. Thus 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 neutralizes 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 diph- 

 theria bacilli, beyond what a normal serum would do, there- 

 fore 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 pres- 

 sence of a small quantity of demonstrable protective sub- 

 stance in the blood. These are, however, peculiar and ex- 

 ceptional cases. 



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



f "Ann. de 1'Inst. Pasteur," vm, p. 615, 1894. 



J "Jour, of Experimental Medicine," July, 1896, i, No. 5. 



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



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



