IMMUNITY IN PNEUMOCOCCAL INFECTIONS 9 



immunity, in which they demonstrated that, besides the bactericidal 

 action of the serum, to which they faintly adhered, there was a more 

 important factor at work — phagocytosis brought about under the 

 influence of the serum. " Chez le lapin vaccina, le leucocyte tient du serum 

 son pouvoir d'englober et dHruire le streptocoque" A very short time 

 later Mennes (28), working under the direction of Denys, extended these 

 researches to the pneumococcus, and was able to show that the primary 

 immunising element is in the serum and not in the leucocyte. Highly 

 immune sera were taken and carefully tested for their bactericidal and 

 bacteriolytic power, and in no case was either of these apparent, even 

 after adding quantities of normal serum as a complement. But when 

 leucocytes were added to such sera, the cocci were rapidly picked up by 

 them and underwent a gradual degeration and lysis within them. In 

 many cases the cells were packed full of bacteria, whereas with normal 

 sera the number of bacteria in the phagocyte was comparatively small 



The chief question then arose— Has the serum, as Metchnikoff" and 

 his school believe — a mere stimulating action on the cells, or does it act 

 directly on the bacteria themselves ? 



In 1903- 1904, Wright and Douglas (29) found that the phagocytic 

 property of leucocytes suspended in a serum which has been subjected 

 to a temperature of 60-65° C. is entirely in abeyance, and, on the 

 addition of bacterial emulsions, no phagocytosis takes place. If, 

 conversely, the unheated serum is mixed with bacteria, and digested for 

 fifteen minutes at 37° C, and then subjected to 60° C. for a quarter of an 

 hour, phagocytosis takes place on adding leucocytes. From these 

 fundamental facts it is manifest that some definite substance has passed 

 out of the serum, and attached itself to the bacteria, rendering them 

 suitable pabulum for phagocytosis by the leucocytes. This thermolabile 

 substance they named " Opsonin." 



During the process of active immunisation with staphylococcus, 

 micrococcus melitensis, bacillus tuberculosis, and bacillus pestis, they 

 have been able to show that for these infections the opsonic content of 

 the serum is increased, and have thus demonstrated that, in addition to 

 anti-toxic and bactericidal immunity, there is a third type — opsonic 

 immunity, which is a common phenomenon in a number of infections, 

 and brought about by a coalition and inter-action of the body humors 

 and cells. 



(373) 



