1910.] The Chemical Dynamics of Serum Reactions. 507 
Comparison of these curves (especially that of Dean) with Chart 2 shows 
a marked similarity. Stated shortly, the characteristics of opsonin and 
stimulin reactions are as follows :— ; 
(1) An unheated normal serum induces phagocytosis of organisms by 
leucocytes. 
(2) A heated normal serum induces practically no phagocytosis. 
(3) An unheated immune serum induces strong phagocytosis. 
(4) A heated vmmune serum induces marked phagocytosis. 
The phenomenon of phagocytosis consists of two stages: firstly, approxima- 
tion of the organism to the leucocyte, probably by some amboceptoral action, 
possibly by chance collision; and, secondly, inclusion of the organism by the 
leucocyte. The leucocyte is undoubtedly a source of complement, so there 
may be present a zone of complement in or about it. 
Let us return to the comparison between the curves on Charts 2 and 4, 
presuming for the moment that complement takes part in the reaction. 
If complement acted proportionally to its concentration in the serum, 
then the experiment would appear on a plane erected on the line v = z. 
x=constant 
Fig ce. 
Rearranging equation (8), putting y = x, and extracting roots, we have 
is: C2 +02, /2 (4—32) 
2(z—1) 
y can have only one positive value when z<1 ; 
y has equal roots (z.¢., the summit of the curve) 
when — 82=4 or z= 15. 
Thus if lysis at the summit = 100 per cent., it cannot fall below 75 per cent. 
in the plane (4, y = 2). 
Marshall’s curve, however, falls to 50 per cent. at least, whilst Dean’s falls 
(within the limits of experiment) to 86 per cent. 
Let us now return to.the characteristics (1 to 4) above. 
