12 



Here, then, there is a remarkable want of relationship between the- 

 action of the humours outside the body and within. We are forced to 

 acknowledge that if a factor at all in the production of immunity, the 

 bactericidal property of the humours is not of primary importance, and 

 the next question to be dealt with is how to reconcile the undoubted 

 action "in vitro" with what occurs "in corpore." 



A most, important accompaniment of the clotting of blood and the 

 production of serum is the breaking down of leucocytes, and, as in all 

 the lymph spaces of the body, leucocytes can, and do, enter, so all the- 

 body fluids (as distinguished from the secretions) contain a larger or 

 smaller number of these cells— the blood and lympL the most, the 

 aqueous humour the fewest. Thus all of these body fluids when 

 removed become modified in that now the leucocytes break down and 

 their soluble contents become set free. Can this account for the 

 bactericidal properties of the serum and other fluids ? 



Curiously enough, those who first called attention to those properties 

 were the first to adduce facts in favour of this supposition. Buchner* 

 who, from the beginning, acknowledged that his demouatratiou of the 

 bacteria-killing power of blood serum did not refute, but only modified, 

 the phagocyte theory, showed that if the cells and proteid matter of 

 defibrinated blood were, by keeping, allowed to fall, the serum lost its 

 power, Avhile the layer of corpuscles at the bottom of the vessel possessed 

 it. And Nissenf unwittingly brought forward what is as strong a proof 

 as could be desired in favour of the same contention, a proof to which I 

 have seen no reference, and which I would, therefore, dwell upon 

 in some detail. Blood may be prevented from clotting either by 

 the action of peptone or by adding to it a solution of magnesium sul- 

 phate. In the former case, peptone plasma, as Nissen shows, destroys 

 leucocytes, and this peptone plasma has bactericidal properties as 

 strong, or almost as strong, as ordinary serum ; in the latter case 

 the leucocytes remain intact, but the plasma has absolutely no 

 destructive influence. And so Nissen argued, that in one case the 

 destruction is undergone in the absence of leucocytes, in the other, 

 although leucocytes are present in abundance, no bacteria are killed, 

 hence there is here a proof positive of the correctness of the humoral 

 theory as opposed to that of phagocytosis. But what the experiment 

 proves, and proves most prettily, is that where the leucocytes are 

 prevented from breaking down and liberating their contents, there the 

 plasma has little or no bactericidal action, and that thus the bacteria- 

 killing property of plasma or serum is due to the dissolution of 

 leucocytes. 



* Buchner.—Centmlblatt f. BaKteriologie, 1888, Vol. V. p. 817, and Vol. VI. p. 1 and p. 561, and 

 ArcMv fib- Hygiene, Vol. X., 1890, p. 130. 



f Nlsaen.— Zoc. c't., p. 600. 



