508 Captain A. G. McKendrick. [ Nov. 30, 
The fact that unheated sera act better than heated sera shows that the 
complement of the serum is called into play. 
That a heated normal serum induces practically no phagocytosis, whereas 
a heated immune serum may induce a marked reaction, would suggest that 
the amboceptor (which is present in large quantity in the latter) acts as 
a stimulant on the leucocyte to secrete complement. 
From this point of view Marshall’s curve would lie in the plane 
(z, y = axz—b). Dean’s curve, on the other hand, which is that of a normal 
serum (which when heated would yield practically no phagocytosis), would 
lie either in the plane (2, y = az), or (2, y = ax—b) where 6 is a very small 
quantity. I have calculated this curve, both in planes (z, y = ax), in which 
case the observed value of z with full concentration lies too low, and in the 
plane (z, z = b), in which case the observed value is too high. 
Thus, to summarise, amboceptor and complement both take part in the 
reaction. Complement is supplied by the serum (if this source be available) 
or from the leucocyte, by virtue of stimulation of the cell by the amboceptor— 
a stimulation to secrete complement, which acts locally. 
The curves of Dean and Marshall (Chart 4) are merely further exhibitions 
of the phenomenon of complement “diversion.” (Marshall also gives curves 
of heated immune sera experiments which show the diversion phenomenon.) 
The following points may be of use in calculating curves and finding the 
values of constants in the plane (2, y= az). When y = az, equation (8) 
assumes the form 
ne 5 ene Ca) (17) 
(az—1) 
z has a maximum value when 4 = 3az, or = 1°3/a, and consequently 
f= 202 = : = z has only one positive value when z<1/a. Thus z=1/a 
is the asymptote. | 
Now by the equation (10) y=a/z at the “point of diversion,” and 
consequently in the plane (%,y¥ =ax) a point of diversion occurs when 
z=1/a. Thus if the value of z on the asymptote is known, we know 
its value at the “ point of diversion.” In whole serum experiments y = 2, 
consequently z = 1 at the point of diversion and on the asymptote. 
VIII. The values c and z (Immunity)—(a) ¢ is a constant inversely 
proportional to the amount of y present in the undiluted serum. 
(6) z is a complex factor. It is, from a chemical point of view, the 
amounts of « and y which have been transformed. It is in general the 
effect. It includes, degree of effect, resistance to effect, concentration of stuff 
