
1905.| Substance in Serum which influences Phagocytosis. 523 
3. That in normal serum there is present a substance having a similar 
action and which also resists a temperature of 60° C. for hours, and may 
persist in the serum of the horse for years. 
4, That the experiments recorded in this paper tend to confirm the idea 
that the substances are identical, z.¢., that in normal serum there is present a 
small amount of the immune substance having the property of preparing the 
microbes for phagocytosis. 
5. That cocci fully occupied by the substance from heated immune serum 
when passed through fresh normal serum do not remove the substance from 
normal serum, whereas fresh cocci remove a large part of it. 
6. That the converse of the above is also true, viz., that cocci fully occupied 
by the substance from normal serum do not remove the substance from 
immune serum, whereas fresh cocci do. 
7. That the thermostable substance in normal serum is no doubt identical 
with the “fixateur” or “substance sensibilisatrice ” of the French school and 
with Wright and Douglas’ “ opsonin.” 
Seeing that the terms “ fixateur” and “substance sensibilisatrice ” which 
have been employed by Metchnikoff’s school to include the property of pre- 
paring the microbes for phagocytosis are used to designate a number of other 
properties of immune serum, it may. be convenient to adopt Wright and 
Douglas’ term of “opsonin” for the particular property in question. The 
only danger attached to such a course is that one might be led to regard the 
“opsonin” as actually a different substance and not merely a property of 
immune serum. 
I wish here to express my thanks to Drs. MacConkey and Petrie for the 
kind assistance they have given me in making a large number of the 
enumerations. 
REFERENCES. 
Bordet, J, (1895). ‘‘ Les Leucocytes et les Propriétés Actives du Sérum chez les Vaccinés.” 
‘Annales de l'Institut Pasteur,’ vol. 9, p. 462. 
Bordet, J. (1897). “Contribution 4 ’Etude de Sérum Antistreptococcique,” ‘ Annales de 
l'Institut Pasteur,’ vol. 11, 1897, p. 177. 
Bulloch, W., and Atkin, E. E. (1905). “Experiments on the Nature of the Opsonic 
Action of the Blood Serum,” ‘ Roy. Soc. Proc.,’ vol. 74, p. 379. 
Denys (1897). “ Résultats obtenus par le Sérum Antistreptococcique,” ‘ International 
Medical Congress at Moscow,’ Section III, p. 82. 
Denys and Leclef, I. (1895). “Sur le Mecanisme de l’Immunité chez le Lapin Vacciné 
contre le Streptocoque Pyogéne. La Céllule” (1895), p. 177, vol. 11. 
Hektoen, L., and Ruediger, G. F. (1905). “Studies in Phagocytosis,” ‘Journal of 
_ Infectious Diseases,’ vol. 2, p. 128. 
Levaditi, C. (1901). “Sur Etat de la Cytase dans le Plasma des Animaux normaux et 
des Organismes vaccinés contre le Vibrion Cholérique,” ‘Annales de I’Institut 
Pasteur,’ vol. 15, 1901, p. 894. 
