AGGRESSINS 291 



In applying this method of treatment, by subcutaneous injections, 

 to infections in man, Hiss and Zinsser observed distinctly beneficial 

 results in cases of epidemic cerebrospinal meningitis, in lobar pneu- 

 monia, in staphylococcus infections, and in erysipelas. 1 



In experimenting with the leucocyte extracts in vitro the same au- 

 thors were able to show that precipitates occurred when clear leucocyte 

 extract and the clear extract of various bacteria were mixed. 2 



Further experiments, carried out both in animals and in the test 

 tube, showed that while the leucocytic extracts possessed slight bactericidal 

 powers for a variety of microorganisms, these attributes did not seem 

 sufficient to explain the profound, modifying influences exerted upon 

 bacterial infections by these extracts. Hiss and the writer in their 

 earlier work thought that possibly the action of the leucocytic extracts 

 consisted of the neutralization of bacterial poisons. It is the opinion 

 of the writer at present that it is more likely that these substances 

 favorably influence infection by their action in increasing leucocytosis, 

 or, in other words, non-specific chemotactic action. 



That bactericidal substances can be extracted from leucocytes by 

 various methods has been repeatedly shown by Schattenfroh, Petterson, 

 Korschun, and others. 3 The researches of Petterson as well as, more 

 recently, the work of Zinsser, have shown that these "endolysins," as 

 Petterson has called them, have a structure quite different from that 

 of the serum bacteriolysins in that they are not rendered inactive by 

 temperatures under 80 C., but,' when once destroyed by higher tem- 

 peratures, can not be reactivated either by the addition of fresh serum 

 or of unheated leucocyte extracts. The last-named authors, moreover, 

 have shown that these endocellular bactericidal substances are not 

 increased by immunization, the quantity present in each leucocyte being 

 probably at all times simply sufficient for the digestion of the limited 

 number of bacteria which can be taken up by the individual leucocyte. 



The Problem of Virulence. An extremely obscure chapter in our 

 knowledge of the reaction of animals and man against infection is the 

 one dealing with the questions of varying pathogenicity between differ- 

 ent bacterial species and between different races of the same micro- 

 organism. We know that certain bacteria may be injected into an 



1 Hiss and Zinsser, Jour. Med. Res., N. S., xiv, 3, 1908; ibid., xv, 3, 1909. 



2 Hiss and Zinsser, ibid., xiv, 3, 1908. 



3 Schattenfroh, Arch. f. Hyg., 1897; Petterson, Cent. f. Bakt., I, xxxix, 1905, and 

 ibid., xlvi, 1908; Korschun, Ann. de 1' Inst. Pasteur, xxii, 1908; Zinsser, Jour. Med. 

 Res., xxii, 3, 1910. 



