
1905.] Substance in Serum which influences Phagocytosis, 511 
were employed. The number of ingested cocci were enumerated in 
22 polymorphonuclear leucocytes, and the average taken as the phagocytic 
index. 
Estimations were made of the phagocytosis in the case of animals immunised 
against Staphylococcus pyogenes awreus,* Streptococcus pyogenes, B. typhosus, 
and B. dysenterie. 
These experiments led to a closer study of the nature of the substance in 
serum which assists in the process of phagocytosis ; and to some extent this 
enquiry resolved itself into a study of the relations which the immune sub- 
stance, amboceptor, substance sensibilisatrice, or fixateur, bears to the opsonin 
of Wright and Douglas. For this investigation the Staphylococcus pyogenes 
aureus was chiefly employed owing to the convenience with which emulsions, 
counts, etc., could be made. Two races of the Staphylococcus were used, one 
highly virulent, recently isolated from the human body, the other an old 
laboratory culture. No marked differences were observed in the counts 
obtained from these. 
Where the method of Wright and Douglas has been rigidly employed, the 
results I have obtained have been almost entirely in agreement with theirs. 
I should not feel disposed, however, to place quite the same reliance as they 
do on the numerical accuracy of the results which can be derived from the 
method. Where the leucocytes are very full—z.e., where the counts are high 
—it is impossible to differentiate results by the method of enumeration. In 
this paper differences obtained by all refinements of enumeration have been 
neglected. In all cases an excess of cocci was present. The majority of the 
counts have been made by two or three observers who did not know the 
objects in view, so that personal bias was eliminated. Without entering 
into details, it may briefly be stated that, when using their method, my 
experiments tend to confirm theirs in that there is in normal serum a sub- 
stance which prepares the microbe for the leucocyte; that this substance, or 
“opsonin, as tested by Wright’s method, appears to be destroyed at a 
temperature of 60° C. for 15 minutes, and that the leucocyte is, in a certain 
sense, an indifferent factor. By the employment of other methods, results in 
oppositition to Wright and Douglas’ have been obtained. 
When, however, the question of the thermolability of the “ opsonin ” was 
‘investigated in another manner, the results obtained were opposed to the 
view that the substance was destroyed at the temperatures named by Wright. 
Indeed, it was found that the heated immune sera, even on testing by 
Wright’s method, gave high phagocytic indices. These results suggested a 
re-investigation of the effects of temperature by other methods. 
* Referred to hereinafter as “ Staphylococcus.” 
VOL. LXXVI.—B. 2M 
