THE PHENOMENA OF INFECTION 449 



blood. We say all this seemed clear and probably it is all 

 right, except now it seems probable that although nuclein 

 is abundant in the leukocytes and present in small amount 

 in plasma and serum, it is not the germicidal agent in 

 either. The germicidal agent in the cell and that dissolved 

 in the plasma or serum are both most likely ferments, the 

 one intra- and the other extracellular, and the two are not 

 identical. Metschnikoff s phagocytic theory and Buchner's 

 alexin theory are both in a way right, but whether the 

 germicidal substance in the serum is a secretion of the 

 phagocyte or a disintegration product of the cell is an 

 interesting question. 



The germicidal constituent of blood serum, studied by 

 Buchner and named alexin by him, is inactivated by 

 heating the serum to 55, while the germicidal substance 

 obtained by Kossel and Vaughan from cells, and believed 

 by them at the time to be nucleic acid, required a tempera- 

 ture of 85 to render it inert. Evidently these must be two 

 quite different bodies, or if the same substance, their behavior 

 under the influence of temperature must be markedly 

 affected by the conditions under which they were tested. 

 The researches of Schattenfroth 1 showed further differences 

 between the intra- and extracellular germicidal constituents 

 of the blood. The former has no hemolytic action on the 

 red corpuscles of other species, while the latter may have. 

 The intracellular germicide is not affected by the salt 

 content of the medium, retaining its activity in a salt-free 

 menstruum, while the extracellular substance is inactivated 

 by the removal of salt from the serum by dialysis. Daubler 2 

 came to the conclusion that the germicidal constituents 

 of the serum and of the leukocytes are not identical, the 

 latter remaining active after being heated to 60. He also 

 found that the germicidal substances obtained from the 

 leukocytes of different species differ in measurable degree 

 as tested upon the same bacteria. Many other investi- 



1 Archiv f. Hygiene, 1897, xxxi, 1; ibid., 1899, xxxv, 135. 



2 Centralbl. f. Bakt., 1899, xxv, 129. 



