CHAPTEE XX. 



OPSOKLNTS. 



Although the importance of the influence of 

 the serum in phagocytic processes was recognized 

 by Denys and Leclef , it remained for Wright and 

 Douglas to demonstrate that substances exist in 

 the serum which are capable of rendering bacteria 

 susceptible to phagocytosis. The name opsonin 

 which they applied to this substance has come 

 into general use. 



The proof of the action of opsonin on bacteria 

 was based on the following facts: 1. When the 

 fresh defibrinated blood of some animal is mixed 

 with the culture of a suitable micro-organism 

 (staphylococcus, streptococcus, anthrax bacillus, 

 etc.) and placed in the thermostat for 20 or 30 

 minutes, stained preparations of the mixture show 

 that the polymorphonuclear leucocytes contain a 

 large number of the microbes. 2. If, however, all 

 the serum is washed from the blood before adding 

 the micro-organisms, practically no bacteria are 

 ingested. This shows the importance of the serum, 

 but does not differentiate between some effect on 

 the leucocytes, on the one hand, or the bacteria, 

 on the other. 3. In order to decide this point one 

 may subject the suspension of bacteria to the 

 action of fresh cell-free serum, and after a contact 

 of about 30 minutes remove all the serum by cen- 

 trifugation, and mix the "sensitized" culture with 

 serum-free blood; phagocytosis occurs almost to 



