264 ROYAL SOCIETY OF CANADA 



salt solution are mixed together, placed in the incubator for fifteen 

 minutes at 37° Cent. A film is made from this on ^ glass slide, 

 stained by a modified RomanofEsky method, and the number of bacteria 

 ingested by the leucocytes is determined. The bacteria contained within 

 twenty cells are counted and an average struck per cell. The authors 

 find that the leucocytes have no power to engulph bacteria unless the 

 latter have previously been sensitized by contact with blood serum. 

 Conversely, serum loses its sensitizing power if it be heated to 60° to 

 .05° for fifteen minutes. Clearly, then, the serum contains some sub- 

 stance of fundamental importance in determining the fact of phagocy- 

 tosis. These opsonins, as they are called, are thermolabile, and, accord- 

 ing to Wright and Douglas, act by effecting some change in the bacteria 

 and not by directly stimulating the activities of the leucocytes. These 

 observations have been amply confirmed by later observers, notably, 

 Bulloch and Atkin, Hektoen and Euediger, and Dean. In the case of 

 the sera of animals immunized against certain infections, it has farther 

 been shown that opsonins are present in the blood in increased amounts, 

 and, moreover, as a result of the inoculation of bacterial toxins the 

 opsonic content of the blood can be increased. Some doubt still exists 

 as to the nature of these opsonins of "Wright and Douglas. Dean, for 

 instance, holds that -opsonins are thermostable and, therefore, are to be 

 identified with the specific " immune body," " fixateur," or " substance 

 sensibilisatrice," previously described by other observers, as Denys, 

 Metschnikoff, Savtschenko, and Levaditi. The question arises whether 

 the opsonins of normal blood serum are identical with those of immune 

 sera. Dean's work would tend to confirm the idea that they are. 

 That normal sera contain an immune substance has, of course, been 

 known for some time. The normal antitoxin (e.g.. of diphtheria) 

 and antiferments need only be mentioned. The observations of Pfeiffer, 

 Bordet, Moxter, Ehrlich, and ]\rorgenroth, have firmly established the 

 fact that the bacteriolytic and hannolytic actions of normal sera are 

 due to the presence in the sera of an immune body plus a complement. 

 With regard to opsonins, it is -still undetermined whether free comple- 

 ment may take part in the preparation of the microbes, but Dean's 

 work goes to show that this at all events is not a necessary factor in 

 the case. 



It would be interesting to know% as tending to elucidate the ques- 

 tion where the opsonins originate, if there be any relationship bet^veen 

 the increased number of leucocytes so often found in the blood in 

 Qiost infectious diseases and the amount of opsonin in the blood. Our 

 knowdedge at present is not sufficient to give a decided answ'er to this 

 important question. The experiments of Bulloch and Ledingham with 



