OPSONINS AND VACCINE THERAPY 349 



which may depend upon a variety of influences which have been 

 discussed in another section and need not be recapitulated. Suffice 

 it to say that variations in the susceptibility of inoculated subjects 

 do not, in any way, furnish a sufficient explanation for these 

 phenomena. 



In an effort to cast light upon this subject, Bail, following in the 

 footsteps of his predecessors, Kruse, 30 Deutsch and Feistmantel, 31 

 has formulated his so-called ' i aggressin-theory. " 



Bail 32 was first led to the formulation of his theory by extensive 

 researches which he had made in conjunction with Petterson 33 into 

 anthrax immunity. He had noted, as others before him had, that 

 animals, highly susceptible to anthrax, often possessed marked bac- 

 tericidal powers against this bacillus. When such animals, whose 

 serum should surely be capable of bringing about the death of, at 

 least, a few hundred anthrax bacilli, were injected with doses far 

 less than this number they nevertheless succumbed rapidly and the 

 bacilli multiplied enormously in their bodies. He argued from this 

 that the injected microorganisms must possess some weapon whereby 

 they were enabled to counteract the protective forces of the animal 

 organism. In an anthrax-immune animal, as a matter of fact, no 

 proliferation of bacteria took place and the injected germs were 

 rapidly disposed of by the protective forces, foremost of which was 

 phagocytosis. 



The theory of Bail 34 contains the following basic principles: 35 



Pathogenic bacteria differ fundamentally from non-pathogenic 

 bacteria in their power to overcome the protective mechanism of 

 the animal body, and to proliferate within it. They accomplish this 

 by virtue of definite substances given off by them, probably in the 

 nature of a secretion, which acts primarily by protecting them 

 against phagocytosis. These substances (referred to by Kruse as 

 "Lysins") were named by Bail, * * Aggressins. " The production of 

 aggressins by pathogenic germs is probably absent in test-tube cul- 

 tures, or, at any rate, is greatly depressed under such conditions, 



30 Kruse, Ziegler 's Beitrage, xii, 1893. 



31 Deutsch und Feistmantel, "Die Impfstoffe in Sera," Leipzig, 1903. 



32 Bail, Cent, f . Bakt., I, xxvii, 1900, and xxxiii, 1902. 



83 Bail und Petterson, Cent. f. Bakt., I, xxxiv, 1903; xxxv, 1904; xxxvi, 1904. 

 34 Bail, Arch, f . Hyg., lii, 1905 ; liii, 1905 ; Wien. klin. Woch., xvii, 1905. 

 85 Bail und Weil, Wien. klin. Woch., ix, 1906; Cent. f. Bakt., I, xl, 1906; xlii. 

 1906. 



