106 PATHOGENIC BACTERIA. 



ring 1 also immunized mice by injecting them with the 

 blood of the rat, and found them proof against anthrax; 

 and Hankin 2 not only protected mice in the same way, 

 but also by injecting them with an albumose extracted 

 from the spleen of the rat. 



Abel 3 has found that the blood serum of healthy men 

 sometimes affords protection against diphtheria toxin; 

 Stern has found one normal serum capable of protecting 

 against the germ of typhoid fever, and Metschnikoif, one 

 against cholera. Fischel and Wunschheim 4 found that 

 new-born babies are immune to diphtheria, probably be- 

 cause of a protective substance in the blood. Bolton 5 

 has found a presumably normal horse whose blood was 

 markedly antitoxic to diphtheria. 



These observations of antitoxin-like substances oc- 

 curring in natural immunity, when considered by them- 

 selves, are very suggestive. Unfortunately, however, 

 they are outweighed by the negative observations, and 

 it must be admitted that as a rule natural immunity is 

 not accompanied by the occurrence of demonstrable an- 

 titoxin in the blood. 



All protective and neutralizing energies may not of 

 necessity be antitoxins in the accepted meaning of the 

 term, and it is not impossible that the blood of an animal 

 may contain toxin-neutralizing substances of some dif- 

 ferent kind whose demonstration may be made difficult 

 or impossible because of their failure to act when intro- 

 duced into other animals. 



Hankin 6 has divided the protective proteids — alexins 

 — into groups accordingly as they are found in animals 

 with natural or acquired immunity. Those occurring in 

 naturally immune animals he calls sozins ; those in 

 acquired immunity, phylaxins. These proteids are sus- 



1 Loc. cit. 2 Loc. cit. 



3 Hueppe's Principles of Bacteriology, translated by E. O. Jordan, p. 374. 



4 Zeitschrift fur Heilkunde, 1885, xvi., 429-482. 



5 Journal of Experimental Medicine, July, 1896, vol. i., No. 3. 



6 Loc. cit. 



