Note 284 — Chapter VII · THE MECHANISM OF NATURAL IMMUNITY AGAINST MICRO-ORGANISMS

Since Nuttall’s first paper appeared a certain bactericidal action of the aqueous humour has been observed. This fact should be taken into consideration in the study of the question of the phagocytic origin of the bactericidal substance of the body fluids. If this substance really comes from the phagocytes, it should not be found in the transparent aqueous humour that contains no, or almost no, leucocytes. Now this fluid sometimes destroys a certain number of micro-organisms. This apparent contradiction is explained by the fact that the bactericidal action may be exercised by all kinds of fluids, such as physiological salt solution, nutritive broths, etc. The bactericidal property of the aqueous humour comes into this category. Its action is, as a rule, much more feeble than the action of serums and exudations and is not modified by heating to 55°–56° C. In certain aqueous humours, a little cytase, or true bactericidal substance, may come into play, for we find aqueous humours which coagulate and which, when centrifugalised, show a small deposit of leucocytes. These results have been obtained by Mme. Metchnikoff.

It must not be forgotten also that, even in the bactericidal action of blood serums, a certain factor is the change of medium which the micro-organisms experience with the plasmolytic phenomena which follow. But it is not possible to ascribe to this factor the whole of the bactericidal property of serums and exudations, as is done by Baumgarten (Arb. a. d. pathol.-anat. Inst. zu Tübingen, 1899, Bd. III, S. 1, and Berl. klin. Wchnschr., 1900, SS. 136, 162, 192), and his pupils Jetter and Walz supported by A. Fischer (Ztschr. f. Hyg., Leipzig, 1900, Bd. XXXV, S. 1). The idea of reducing the destruction of bacteria in serums and exudations to the effect of osmotic pressure has been recently elaborately analysed by v. Lingelsheim (Ztschr. f. Hyg., Leipzig, 1901, Bd. XXXVII, S. 131). With great justness he comes to the conclusion that “the existence in extravascular blood or in serum, of bactericidal substances acting as soluble ferments can now no longer be denied” (p. 167). In studying this question we must not lose sight of the fact that these bactericidal substances (alexines, complements, or cytases) give rise to the production in the animal organism of antagonistic substances as described by us in the 5th Chapter.