1907.] Substance in Serum which influences Phagocytosis. 403 



A striking instance may be given here. One specimen of an anti- 

 staphylococcic horse serum, when diluted 32 times with saline, was found to 

 have lost only 25 per cent, of its sensitising power, whereas the corresponding 

 dilution of a normal serum of the same age had lost 90 per cent. 



This subject in its various aspects will be dealt with more fully upon 

 a future occasion.*f 



The Influence of the Addition of Fresh Serum upon the Opsonic 

 Power of Heated Immune Serum. 



As was pointed out in my previous communication, thermostable immune 

 substance is capable of sensitising the microbes for phagocytosis in the 

 absence of free complement. Metchnikoff's view, that in such cases the 

 complement may be supplied by the leucocytes, is a possible interpretation, 

 but will not be dealt with in the present paper. I propose to discuss here 

 the question as to whether the heated immune substance in the presence of 



* Some misunderstanding (Wright and Reid, i Roy. Soc. Proc., ; 1906) has arisen in 

 regard to my remarks (' Roy. Soc. Proc.,' vol. 76, p. 506; on the limitations of Wright and 

 Douglas' technique. I would again point out that their method may fail to demonstrate 

 sensitising substances where these are present in considerable amount, and may show no 

 difference between two fluids, notwithstanding that one contains a large amount of 

 sensitising substance, the other only a small amount, or none. 



To illustrate this, I may quote some experiments which were carried out with the view of 

 determining the limits of sensitising action in an immune staphylococcic serum. Dilutions 

 of 1 in 100 of this immune serum, and 1 in 100 normal serum, when tested by the ordinary 

 technique of Wright and Douglas, showed no difference in their action, which was 

 practically nil. On the other hand, if one mixed a volume of these dilutions with an 

 equal volume of a coccal emulsion, so that the ultimate dilution was 1 in 200, and placed 

 the mixtures at 35° *5 C. for one hour, and, after re-emulsifying both, carried out the 

 ordinary technique, a very marked difference could be determined. The results obtained 

 with the same sera, at an interval of some months, by three different observers, who 

 endeavoured to adhere to standard conditions as to emulsions, etc., were as follows : — 



(1) 



Phagocytic index of 



Normal serum. 



Immune 



staphylococcic 



serum. 



2 4 

 3-3 



1-9 



21 



18 7 

 23-7 



(2) 



(3) 





t After I had made a communication on the effect of dilution at the Pathological Society 

 of Great Britain and Ireland, a paper by Simon, Lamar, and Bispham, which deals with 

 the importance of this subject of dilution, came into my hands. 



