THE OPSONIC METHOD 213 



present, the latter being quite specific. That is to say, in 

 the process of immunisation specific opsonins are formed 

 and the increase of opsonins following injection of a vaccine 

 is probably due to the formation of immune opsonins which 

 react specifically. 



Muir and Martin 1 believe that in immune serum a specific, 

 immune, thermostable opsonin is present, and also a 

 normal, thermolabile opsonin. 



Wright considers the opsonins to be substances distinct 

 from all others, but MetchnikofT, Dean, and other observers 

 suggest that they are identical with the " substance 

 sensibilisatrice." 



It is doubtful if opsonins are present in more than 

 traces in the unaltered blood plasma : like alexins, they 

 seem to develop as a result of coagulation. The role of 

 opsonins in immunity and in recovery from infection is 

 therefore a complex problem. 



The opsonic method has been criticised of late. Thus Moss 2 

 says : " None of the present methods of estimating the opsonic 

 content of the blood seems sufficiently accurate to be of practical 

 value " ; Fitzgerald, Whiteman, and Strangeways, 3 in an elaborate 

 investigation, concluded that the method is unreliable. Whereas 

 Wright takes into account the serum only, Shattock and Dudgeon 4 

 state that " the cells (i.e. the phagocytes) vary in value like the 

 serum." It may be granted that the whole truth respecting the 

 opsonic reaction and method is not yet fully known, but many of 

 the criticisms have been based on an imperfect technique. On the 

 whole, it may be said that Wright's method, with careful technique 

 and in practised hands, gives information previously impossible to 

 obtain, and the proper dosage of, and treatment by, vaccines has 

 been largely elaborated by means of it. 



1 Proc. Roy. Soc. Lond., B. Ixxix, 1903, p. 187. 



2 Johns Hopkins Hosp. Bull., vol. xviii, 1907, p. 237. 



3 Bull. Committee, for the Study of Special Diseases (Cambridge), vol. i, 

 1907, No. 8. 



4 Proc. Roy. Soc. Med., vol. i, 1908, " Medical Section," p. 169. 



