PNEUMOCOCCUS INFECTION 211 



There has been considerable difference of opinion as to the 

 explanations to be given of the facts observed regarding 

 immunisation against the pneumococcus and especially regarding 

 the properties of immune sera. At first these sera were supposed 

 to possess antitoxic qualities largely on the ground that no 

 bactericidal effect was produced by them on the bacterium in 

 vitro. As no specific toxin has been proved to be concerned in 

 the action of the organism the development of an antitoxin 

 during immunisation must, in the present state of knowledge, 

 be looked on as not yet proved. To explain the action of a 

 serum in preventing and curing pneumococcal infections, it 

 has been thought to have the complex character seen in anti- 

 typhoid sera in which two substances immune body and com- 

 plement (see Immunity) are concerned, and the variability in 

 the therapeutic results obtained has been accounted for on 

 the view that there might be a deficiency of complement, such 

 as occurs in other similar cases. The absence of bactericidal 

 effect, however, raises several difficult points. It is stated that 

 no such effect is observable either in immune sera, or in the 

 serum of patients who have successfully come through an attack 

 of the natural disease. Some effect of the kind would be ex- 

 pected to be present if the anti-pneumonic serum were quite 

 comparable to the antityphoid serum. Within recent times 

 many have turned to the opsonic property of sera to account 

 for the facts observed. In this connection Mennes observed 

 that normal leucocytes only become phagocytic towards pneumo- 

 cocci when they are lying in the serum of an animal immunised 

 against this bacterium. Wright had in his early papers looked to 

 the phagocytosis of sensitised bacteria to explain their destruction 

 in the absence of bactericidal qualities in the serum alone, and 

 Neufeld and Bimpau have described the occurrence of an opsonic 

 effect in the action of an anti-pneumococcic serum. Further 

 work may show that along these lines lies the explanation of the 

 facts observed. 



In studying further the relationship of the opsonic effect to 

 pneumococcal infection, inquiry has been directed to the opsonic 

 qualities of the blood of pneumonic patients, especially with a 

 view to throwing light on the nature of the febrile crisis. 

 According to some results the opsonic index as compared with 

 that of a healthy person is not above normal, but if the possible 

 phagocytic capacities of the whole blood of the sick person be 

 taken into account these will probably be much above normal in 

 consequence of the leucocytosis which usually accompanies a 

 successful resistance to this infection. It has been observed, 



