1905. | The Phagocytosis of Red Blood-Cells. 529 
4, The special constituent of serum which possesses the property of inducing 
phagocytosis is destroyed by heating. 
Experiment 14.—The sera of three rabbits which were capable when diluted 
with four parts of saline solution of exciting active phagocytosis of the red 
blood-cells of the hen, calf, and goat respectively, were heated in the dilution 
of 1 in 5 for 30 minutes to 100°C. A slightly milky fluid free from pre- 
cipitate was thus in each case obtained which, on testing, was found to have 
lost its power of causing phagocytosis. The sera of three guinea-pigs, injected 
with red blood-cells of the hen, calf, and rabbit respectively, were similarly 
found to have lost their power of causing phagocytosis, after 30 minutes 
exposure to 100°. 
Experiment 15.—The six sera employed in the preceding experiment were 
heated, undiluted, to 69° for 30 minutes. All remained clear with the 
exception of two of the guinea-pig sera, which became slightly opaque and 
distinctly viscid. With these two no phagocytosis was obtainable; with the 
remaining sera phagocytosis was obtainable, but was not so vigorous as with 
unheated serum. 
It appears, therefore, that while a temperature of 100° rapidly destroys 
the phagocytic action of serum, a temperature of 69° is much less 
effective. 
5. The above characters serve to define the nature of the special con 
stituent of serum which confers upon it the property of bringing about 
phagocytosis of red blood-cells, and show that its rdle is to prepare these 
cells for consumption by leucocytes. It is therefore a member of tke 
group of opsonines first described by Wright and Douglas* in respect of 
bacteria. 
In conclusion, it may be mentioned that erythrocytic opsonines are present 
in relatively small amount in normal sera. Thus, with the inactivated sera 
of the sheep, goat, dove, and hen, phagocytosis of the red blood-cells of the 
calf, goat, sheep, rabbit, and guinea-pig may, by suitably adjusting the 
conditions of experiment, be readily obtained. In the following experiment 
this is illustrated: in A the red blood-cells are insufficiently sensitised, so 
that no phagocytosis takes place, as is also the case in D, where the serum is 
apparently completely deopsinated; in F, on the other hand, owing to the 
relatively small amount of red blood-cells employed, the serum employed 
still retains sufficient opsonin to cause the appearance of phagocytosis when 
fresh red blood-cells are added. 
* “The Léle of the Blood Fluids in connection with Phagocytosis,” ‘ Roy. Soc. Proc., 
1904, vol. 72, p. 357 ; cp. “On the Nature of the Opsonic Action of the Blood Serum.” 
W. Bulloch and E. E. Atkin, ‘Roy. Soc. Proc.,’ 1905, vol. 74, p. 379. 
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