i68 THE PRINCIPLES OF IMMUNOLOGY 



extracellular destruction is accomplished by identical destructive 

 agents. The demonstration that extracellular destruction of bacteria 

 (bacteriolysis) requires the participation of amboceptor and comple- 

 ment had little influence on Metchnikoff's views, inasmuch as he was 

 convinced that complement originates solely in the leucocytes. As we 

 have stated (page 129) the more recent examination of this problem 

 makes it certain that complement exists free in the blood. Further 

 study, more particularly of opsonins and bacteriotropins, has made 

 it apparent that the mechanism of intracellular digestion is quite differ- 

 ent from that of extracellular lysis. Nevertheless, the leucocytes may 

 contribute to the extracellular destruction of bacteria. Buchner showed 

 that the exudation, produced in the pleura of rabbits and dogs by injec- 

 tions of aleuronat, removed and killed by freezing and thawing, pos- 

 sesses the property of killing bacillus coli. Denys and Kaisin produced 

 pleural exudates by injection of killed staphylococci and removed the 

 cells by centrifugation. The clear supernatant fluid was actively bac- 

 tericidal. Others have made extracts of exudates, and of leucocytes 

 obtained from the blood, and have demonstrated that a bactericidal 

 substance is to be obtained. Certainly these substances are yielded up 

 after the destruction of the cells and, according to Petterson, they 

 may be secreted by the cell during its life. The substances are resistant 

 to a temperature of 56 C., but after inactivation by heat to 75 to 80 

 C. they cannot be reactivated by the addition of fresh extracts. This 

 substance or group of substances has been called endolysin by Petterson 

 and leucine by Schneider. It is not identical in all animals since that 

 from dogs, rabbits and guinea-pigs kills bacillus proteus and bacillus 

 anthracis, but that from the guinea-pig and cat fail to kill the bacillus 

 typhosus and the spirillum cholerae. 



Bachmann has recently reported on a so-called leucocyte antibody, 

 " antkorps leucocytaire," which is distinct from the bactericidal endo- 

 lysin. It appears in the leucocytes of immunized animals and may serve 

 to produce passive immunity in other animals. It is found only in the 

 polymorphonuclear leucocytes and may be extracted in normal serum. 

 It is effective in protecting guinea-pigs against intraperitoneal injection 

 of the specific organism and also acts beneficially and specifically upon 

 established infections. A temperature of 75 C. destroys this substance, 

 but if the material is well diluted and gelatin added, the same degree 

 of heat serves to destroy the non-specific bactericidal substances (endo- 

 lysins) but permits the specific leucocyte antibody to remain active. 

 Bachmann believes that the persistence of this antibody in the leuco- 

 cytes explains the fact that individuals retain immunity to certain 

 diseases after the serum antibodies are no longer demonstrable. 



Leucocyte Enzymes. In contrast to the bactericidal substances 

 extracted from leucocytes it is possible to obtain enzymes. Leber, in 

 a study of inflammation, found that sterile pus can liquefy gelatin and 

 the study of this proteolytic enzyme, the leucoprotease, has been ex- 

 tended by Miiller and Jochmann, Opie, Longcope and others. This 

 leucoprotease may be purified by precipitation with alcohol more par- 



