520 Mr. G. Dean. On the Nature of the [July 8, 
with which a bacterial field is cleared of micro-organisms suggests such an 
occurrence. 
An interesting observation was made in this connection, viz., that organisms 
after being stained with fuchsin, which has a strong agglutinating action, 
were capable of ingestion, whereas the same organisms killed by heat were 
refused by the leucocyte. 
It was observed that the normal serum of the same horse heated to 60° C. 
for 20 minutes had a considerable “opsonising” action on the typhoid 
bacillus, whereas it had little effect on the dysentery bacillus. Twenty-two 
typhoid bacilli were ingested per leucocyte compared with 1:5 dysentery 
bacilli. 
Summary and Remarks. 
An immune staphylococcic serum obtained from the rabbit when heated to 
60° C. still contains a substance capable of preparing the cocci for phago- 
cytosis. An identical result was obtained in the case of an immune staphylo- 
coccic serum from the horse. Efforts were made to ascertain whether this 
substance was identical with the substance in normal serum giving rise to the 
same effect, ve, to the “opsonin” of Wright. It was found that when the 
cocci were added to a fairly large volume of normal serum which had been 
heated to 60° C. for 20 minutes, incubated for 15 minutes and centrifugalised, 
they were rapidly phagocyted. 
It appeared, therefore, that the heating to 60° C. had produced only a 
fractional destruction of the opsonin, which in the case of normal serum was 
present in such small amount that it was no longer measurable by Wright 
and Douglas’ method. 
This view was confirmed by heating for various periods both normal and 
immune serum and comparing the fall resulting. The curves obtained in 
both cases were similar. The serum of various animals, the goat, rabbit, 
horse, guinea-pig, rat, and human were tested for the thermostability of the 
substance. In all it was found to be thermostable when tested in the way 
mentioned, but more of it appeared to be present in the serum of the horse 
than in the serum of, eg., man and rat, since in the case of the horse it was 
found to be present, after heating, in an amount which was still capable of 
being demonstrated by Wright’s method. Horse serum heated for four hours 
to 60° C. still contained a large amount of the substance. 
Experiments were carried out with the view of ascertaining the relation of 
the substance in normal serum to the substance in immune serum. 
Cocci which had been prepared by contact with normal serum so that they 
were probably fully occupied by the substance were passed through heated 
