514 Mr. G. Dean. On the Nature of the [July 8, 
These experiments show that in an immune Staphylococcic serum enough 
of the substance remains undestroyed by heating to be demonstrable by the 
use of Wright’s method. 
When fresh serum, either normal or immune, is heated to 60° C. for various 
periods, one finds that, as estimated by Wright and Douglas’ method, there 
is a great fall in the first two minutes, and after that the curves run almost 
parallel to the base line. In the case of normal serum the fall is so great 
that the curve may reach the base line. 
The accompanying chart gives a graphic representation of what happened 
flee ea Neleaned Be 
Ab Eee ee 
Sa 
iS il 12 3 Iq Is) te 
SMianeess 
50 






AS 
40 

35 
30 
25 
Cocci per 
p. eee 
on heating a normal rabbit’s serum and an immune Staphylococcus rabbit’s 
serum for different periods up to 16 minutes. The number 50 applied to the 
original strength of the immune serum is only approximate, as in such high 
counts accuracy is impossible. It will be seen that after one minute’s heating 
the immune serum fell to about 18 cocci per leucocyte, and, allowing for 
experimental errors (the average of a large number of counts was taken), it 
then runs parallel to, the base line. 
The normal serum fell from 20 to 5 at the end of the first minute, to 1 at 
the end of the second minute, and then ran almost parallel to the base line, 
the average phagocytic index of a number of counts being about 0°5. 
The results after 30 minutes showed that no great change had occurred. 
One must remember that Wright and Douglas’ method probably demon- 
strates the presence of the “opsonin” over only a very short range. The 
brief time during which the substance is allowed to act on the cocci probably 
admits of only fairly high concentrations being indicated. If one compares 
