W. F. Harvey and A. M^Kendrick 
83 
when the emulsion remained concentrated. It is frequently stated that a higlily 
agglutinating serum may contain no opsonin, but before any such statement is 
accepted we require to know whether it holds good (a) on successive dilution of 
the serum, (b) on successive dilution of the emulsion. Our example serves to show 
that agglutination may play a large part in vitiating the comparability of indices. 
But agglutination may be slight and test sera may not be so active as the one 
here used. Therefore it again becomes necessary to determine, for agglutinating 
sera of all grades, what limitations agglutination imposes on the comparability of 
indices. It must also be evident that this factor must be a varying one for 
different laboratories. 
Example 3. One of the remai kable features of an opsonic frequency distribution 
is the variability or degree of dispersion exhibited. Sir Almroth Wright has 
suggested that this may be due in part at any rate to unequal opportunity for 
phagocytosis. Leucocytes and red blood corpuscles are heavy as compared with 
bacteria, and tend rapidly to settle down. Although the capillary tubes are placed 
horizontally in the opsoniser, there will nevertheless be a certain amount of settling 
and deposition in layers. Those leucocytes in the lowest layers will have much 
less opportunity to ingest bacteria than the topmost ones. Consequently we may 
expect to get every degree of ingestion from those containing no bacteria up to 
those containing as many as they can take up in the time, and with the particular 
concentration of emulsion. Now if we could keep the tubes in constant rotary 
movement, we might expect on the above hypothesis that the degree of variation 
would be greatly reduced, and this is what does happen : but instead of finding 
that all the leucocytes, as on the basis of equal opportunity they should, had taken 
up more or less the same number of bacteria, we find that the diminution in varia- 
bility has been brought about by an increase in the number of those leucocytes 
which have taken up few or no bacteria at the expense of those which took up 
many. Of course, we could scarcely expect to find in any form of experiment that 
all leucocytes had taken up nearly the same number of bacteria, for leucocytes 
are themselves living organisms showing, in any one sample, all the stages of 
development, maturity and decay, correlated with which we should be prepared 
to find a variable phagocytic activity. Still the diminution of variability of this 
experiment was probably to be traced to mechanical interference with phagocytosis 
due to the turning movements. The tubes were not turned continuously, but given 
a half-twist every 60 seconds. The organism used was the Streptococcus foecalis 
and the emulsion a thick one. The test serum was highly opsonic, giving in 
the course of routine examination an index of 2'14 on the day previous to this 
experiment. See Table on p. 84. 
Exaviple 4. To test whether it is immaterial if organisms adhering in couplets 
or triplets should be counted as 2's or 3's or as single organisms in the estimation 
of an index. The organism taken was the Streptococcus foecalis, which, together 
with the immune serum, was kindly supplied to me by Dr Matthews. This 
organism makes a fairly good emulsion and the clumps remaining are not greater 
11—2 
