PHAGOCYTOSIS 257 



is logical, complete, and well supported by evidence, but it does 

 not take into account the more recent work of Sir Almr.oth 

 Wright and his followers, and this now calls for discussion before 

 the role of phagocytosis in immunity can be profitably discussed 

 further. 



It may be admitted that Wright did not discover the fact that 

 serum may aid phagocytosis by acting on the bacteria ; this had 

 been already shown by Denys and Leclef in 1895, by Mennes 

 and by Markl. And Neufeld and Rimpau had carefully investi- 

 gated the same property in the serum of animals immunized to 

 streptococci and pneumococci, and had described their bacterio- 

 tropic substances, which are apparently identical with what we 

 now know as thermostable opsonins. This does not detract in 

 the least from the credit due to Wright, who by devising a simple 

 quantitative method of examination, readily applicable in clinical 

 medicine, made a very great advance in our knowledge of the 

 theory of the subject, and has added a most important and useful 

 method of examination of the blood. The credit for the intro- 

 duction of the use of vaccines in the treatment of established 

 disease (as opposed to its prevention) is, of course, due to him 

 alone. 



The name opsonin (opsono = I cater for, I prepare for food) is 

 given to substances which occur in the serum and have the power 

 of preparing bacteria and other cells for ingestion by the leuco- 

 cytes, and which are, or are held to be for there is no absolute 

 proof different from the substances which we have previously 

 considered. We shall discuss this question of identity or non- 

 identity subsequently, and shall be content at present with saying 

 that, whereas bacteria that have been exposed to the action of 

 alexin are, or may be, obviously injured, a bacterium may be 

 saturated with opsonin without being injured in the least, and 

 may still retain its viability and virulence uninjured. 



The fundamental experiments of Wright and Douglas were of 

 this nature, and they are easy to repeat and unimpugnable in 

 accuracy. An emulsion of leucocytes, free from serum, is pre- 

 pared by receiving blood in normal saline solution containing 

 citrate of soda, centrifugalizing, removing the supernatant fluid 

 and replacing it with saline solution, mixing and recentrifugalizing. 

 This process must be repeated until all trace of serum is removed, 

 and the top layer of the deposit is then pipetted off, and will be 

 found to be rich in leucocytes. 



