528 Dr. J. O. Wakelin Barratt. [July 14, 
serum. On testing the phagocytic power of the serum by adding to it, at the 
end of three hours, leucocytes from the rabbit and red blood-cells from the 
calf, it was found that at the end of one hour, at 37°, about 25 per cent. of 
the leucocytes had taken up one to four red blood-cells. 
Hapervments 12 and 13.—These were similarly carried out with the serum 
of guinea-pigs, which had received intraperitoneal injections of red blood-cells 
of the calf and rabbit respectively. After the sera had been treated for three 
hours at 37° with an equal bulk of leucocytes from the guinea-pig, it was 
found on testing their phagocytic power that, at the end of an hour, 20 per 
cent. and 75 per cent. respectively of the leucocytes had taken up red blood- 
cells. 
The réle of the leucocytes, therefore, appears to be passive so long as the 
substance in question remains free in the serum, and only when a combination 
with red blood-cells has occurred do the leucocytes proceed to ingest the 
latter. Moreover, in experiments upon phagocytosis leucocytes other than 
those of the animal employed for injection of red blood-cells, may often be 
used. Thus it was found that when rabbits had been injected with red blood- 
cells from the hen or guinea-pig, their sera induced phagocytosis of red 
blood-cells of the kind injected, when leucocytes from the guinea-pig, goat, 
or sheep, instead of the rabbit, were used for experiment. In the same 
way with serum obtained from a goat injected with red blood-cells of 
the sheep, phagocytosis of the latter 7 witro could be obtained with 
leucocytes from the rabbit, guinea-pig, sheep, or dove; and such examples 
can be multiplied. 
3. When red blood-cells which have remained for some time in a serum 
capable of bringing about phagocytosis in vitro, are very thoroughly washed 
in 0°85 per cent. sodium chloride solution and then added to leucocytes 
suspended in saline solution, rapid phagocytosis may be obtained though the 
fluid employed is free from serum. It is essential in experiments of this kind 
that the serum used does not agglutinate the red blood-cells, for when the 
latter are heaped together phagocytosis cannot be satisfactorily observed. 
With the sera employed for Experiments 8 and 9, no agglutination occurred 
when red blood-cells from the calf and rabbit respectively were allowed to 
remain in four times their bulk of serum for one hour at 37°. After washing 
in saline solution and adding guinea-pig leucocytes, it was found ‘that, at the 
end of 30 minutes at 37° C., 20 to 25 per cent. of the leucocytes had each 
taken up one to four red blood-cells. Still more rapid phagocytosis was 
obtained with red blood-cells of the calf and goat which had been similarly 
sensibilised with sera obtained from rabbits which had previously been several 
times injected with these varieties of red blood-cells. 
