224 Dr. A. E. Wright and Staff-Surgeon S. T. Reid. [Oct. 21, 



throughout almost as high a phagocytic count as the serum which had been 

 kept in the dark, in the case of the heated samples the serum which had 

 been exposed to sunlight gave a zero result, while the specimen which had 

 been kept in the dark gave a count of 2*3 bacilli to each leucocyte. 



Comment. — The experiment shows that the reputedly thermostable opsonin 

 is — in contradiction with what is known to hold of other thermostable 

 elements — eminently heliolabile. 



Conclusions with respect to the Nature of the Incitor Element ichich is found in 

 Heated Immune Serum after it has been Exposed to Heat. 



Manifestly the plain teaching of our experiments is, that the opsonin 

 which is found in the heated immune serum of a patient who has responded 

 to tubercular infection, or as the case may be to the inoculation of a 

 tubercle vaccine, does not differ with respect to its resistance to heat and 

 sunlight from the opsonin which is found in the unheated normal serum. 



A precisely similar conclusion with respect to the identity of the 

 opsonins found respectively in unheated normal and heated immune sera 

 was, we may note, arrived at by Dean in connection with his experiments 

 on the sera of animals which had been immunised against staphylococcus. 



We have only to remark in conclusion that if we prefer to speak of the 

 opsonin as a thermolabile element, and Dean prefers to speak of it as 

 a thermostable element, there is nothing at issue between us except the 

 question as to whether it is in harmony with usage, and with the genius of 

 the English language as employed in scientific discourse, to characterise 

 as " thermostable " an element of which at best residual traces remain 

 in the case of the normal serum where this has been heated to 60° C, and 

 in the case of the immune serum where this has, after adequate dilution, 

 been heated to the same temperature. 



Appendix. 



It may be convenient to subjoin here, in tabular form, the residts of three 

 experiments, similar to that set forth in Curve V, in which the opsonic power 

 of a tuberculo-immune serum was measured' in a series of dilutions made in 

 the one case after the serum had been heated to 60° C. for 10 minutes, and 

 in the other case before the serum was so heated. 



