PATHOLOGY OF PNEUMOCOCCUS INFECTION 241 



protecting animals against pneumococcal infection. These 

 must at present be looked on as the bodies concerned in the 

 curative action of anti-serum. With regard to them Neufeld 

 and Haendel insist that the concentration in the patient's blood, 

 rather than the amount present in the body, is the important 

 factor. There is experimental evidence that when the concentra- 

 tion is above a certain degree an enormous number of pneumo- 

 cocci can be successfully disposed of, while with a concentration 

 below this limit. a relatively small dose may prove fatal. As 

 bearing on the factors involved in the successful resistance of 

 the organism to the pneumococcus, it has been noted that 

 avirulent pneumococci are more readily opsonised than more 

 virulent strains. It is further stated that avirulent cultures of 

 the pneumococcus can be made to resist phagocytosis if they are 

 treated with the products of the autolysis of virulent strains or 

 with washings from such strains, and that virulent cocci if 

 washed with saline become capable of being readily phagocyted. 

 While it cannot be stated definitely that the opsonic qualities 

 of the serum are the essential factors in resistance to the 

 pneumococcus, it is probable that the activities of the leucocytes 

 play a part in the process. It has long been known that 

 a leucocytosis occurs in the disease, and the degree of this is 

 related to the outlook in the case. Thus, a low leucocyte count 

 when correlated with the clinical symptoms indicates either a 

 mild infection or a grave condition in which resistance is 

 deficient. A count of over 10,000 per c.mm., progressively 

 increasing, is a favourable sign in an uncomplicated pneumonia. 

 The part played by the leucocytes has also been investigated 

 experimentally by rendering the bone-marrow aplastic by means 

 of benzol ; under such circumstances the resistance of the animal 

 to infection is diminished (Winternitz and Kline). 



A substance derived from the infecting pneumococcus some- 

 times appears in the urine during pneumonia. It gives a 

 precipitin reaction with the anti-serum corresponding to the 

 type of pneumococcus causing the infection, and can be 

 detected by mixing equal quantities of clear centrifuged urine 

 with an equal amount of the anti-serum ; this method can, in fact, 

 be used for determining the type of pneumococcus present in the 

 body. The appearance of this substance in the urine is an 

 indication that the case is a severe one, and a progressive increase 

 in amount is a bad prognostic sign. 



It may be noted here, in conclusion, that in man immunity 

 against pneumonia may be short-lived, as in a- good many cases 

 of pneumonia a history of a previous attack is elicited. 

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