510 Mr. G. Dean. On the Nature of the [July 8, 
this effect an “opsonic” effect (“ Opsono,” “I cater for, I prepare victuals 
for”), and they use the term “opsonin” to designate the element in the 
blood-fluids which produces the effect. They find that the “opsonin” is a 
thermolabile body, 2.¢., is destroyed by heating to 60° C. for 10 minutes. 
The leucocyte is an indifferent factor in the matter. 
As a result of inoculation with bacterial vaccines, the amount of the 
opsonin present in the blood may be increased. 
Bulloch and Atkin (1905) have confirmed and extended these results of 
Wright and Douglas. They find that the “opsonin” disappears from serum 
when the latter is mixed with bacteria at 37° C. or 0° C. The action of heat 
is to destroy the “opsonin,”’ and not merely to convert it into a “non- 
opsonisable” modification. It is a simple body, and is not identical with any 
of the antibodies hitherto discovered in the serum. Leishman, at a discussion 
on the subject at the Pathological Society, London, supported the “ stimuline ” 
view of the action of serum. 
Neufeld and Rimpau (1904) find that the immune sera, in the case of the 
streptococcus and pneumococcus do not stimulate the leucocyte in Metchnikoff’s 
sense, but act on and change the micro-organisms, so that they are secondarily 
taken up by the phagocytes. They find that the substance which produces 
this effect is thermostable. A polemic has been waged with Wright as to 
the identity of this body with the “opsonin” (cf Savtschenko and Markl).* 
Hektoen and Ruediger (1905) employed the method of Wright and 
Douglas, and confirm most of their results. They conclude that the “opsonin ” 
has a complex constitution, there being present a haptophorous group, which 
fixes on the microbe, and an opsinophorous group, which produces a physical 
or chemical change in the microbe. 
Introduction to Expervments. 
The present investigation was undertaken with the view of studying certain 
questions as to the relation between the phagocytic immunity which occurs 
in normal animals and in those which have been actively immunised. The 
serum of a number of animals, chiefly horses, which have been immunised 
against various microbes, was examined and compared with the serum of 
normal animals of the same species. At first the method employed was 
Wright and Douglas’, to which reference has already been made. 
To save repetition, it may be stated that in almost every case equal 
volumes of washed leucocytes, of the serum and of the bacterial emulsion 
* The writer had observed the thermostability of the substance in Staphylococcus 
immune serum and in normal serum before hearing of the work of Neufeld and Rimpau. 
Where the term “the substance” is employed in this paper, it is used as an abbreviation 
for “ the substance which prepares the micro-organisms for phagocytosis.” 
