1907. ] | Observations upon Phagocytosis. 169 
melanin? The phagocytosis of melanin was reduced from 18 granules to 
5 granules after saturation of the serum with tubercle bacilli. As it was 
reduced after saturation with melanin from 18 to 6, the reduction is the 
same; 7.¢., the tuberculous serum is deopsonised towards melanin, equally by 
saturation with tubercle bacilli and with melanin. 
How far did the saturation with melanin reduce the phagocytosis towards 
tubercle bacilli? The reduction here is from 170 to 56. It will be noticed 
that the proportion here is very nearly the same as the reduction in phago- 
cytosis towards melanin after saturation with melanin; the phagocytosis is 
reduced to 1/3. 
Although the fall is only from 170 to 56 as compared with that from 170 
to 13 (after saturation with tubercle bacilli), it is clear, nevertheless, that 
a large amount of the “tubercular opsonin” has been removed by the 
melanin; and to this extent the opsonin is not specific to the tubercle 
bacillus.* As already observed the fact than an immune serum can be 
deopsonised by means of melanin shows that melanin can be opsonised. 
The opsonisation and deopsonisation are probably in this case mechanical, 
the finely divided melanin, though inert, entangling or becoming invested 
with the still more finely particulate material of which the opsonin would 
thus appear to consist. 
Question 3.—Will heating an immune serum reduce the phagocytosis 
towards a suspension of melanin in the same way that it is known to do 
towards a suspension of a bacterium causing a disease ? 
~The serum in the four following observations was heated at 60° C. for 
10 minutes :— 
Cases: Erysipelas, acute pleurisy, streptococcus pyzemia, erysipelas. 
Summary and Conclusions from the Observations made to Test the Preceding 
Question. 
The observations show clearly that the phagocytosis of normal cells is 
greatly reduced towards melanin, in immune serum that has been heated, as 
it is towards bacteria. 
This. is a corollary of the observations recorded under Question 1, which 
* Muir and Martin (‘ Roy. Soc. Proc.,’ May, 1907) conclude that there is present in an 
immune serum a specific or immune (thermostable) opsonin, and in addition a normal 
(thermolabile) opsonin. The markedly increased phagocytosis of melanin in immune 
blood would, on such a view, imply that this was due solely to the increase of a “normal 
opsonin.” In the deopsonisation of an immune serum by melanin, the opsonin removed 
would be, on the same supposition, “ normal,” however much increased in amount. The 
authors cited show, indeed, that the thermolabile, “common,” or non-specific opsonin may 
be removed from the same immune serum by various different micro-organisms. 
