IMMUNITY IN PNEUMOCOCCAL INFECTIONS 15 



clinically as acute croupous pneumonia, three gave charts very similar to 

 those of adults ; the others were more or less irregular. 



The significance of the variations in the opsonic content in the serum in 

 acute pneumonia.— In the majority of patients suffering from staphylococcic 

 infections, as furunculosis, sycosis, acne, etc., or tuberculous infections, as 

 phthisis, lupus, Addison's disease, etc., the opsonising power of the serum 

 has been found to be below that of a normal individual. The same 

 is true of pneumococcal infections and in the pre-critical period of acute 

 pneumonia. The critical changes in the course of pneumonia must be 

 regarded as phenomena of immunisation. From the nature of the 

 opsonin it is manifest that, with the rise in the amount of opsonin in the 

 serum, and accordingly in the serum bathing the leucocytic exudate 

 in the pulmonary alveoli and capillaries, more pneumococci are prepared 

 for the leucocytic meal, and they are taken up in greater number, the 

 intoxication of the individual rapidly ceases, and the disordered 

 metabolism is swiftly restored. 



Should, however, the amount of opsonin in the serum fall instead of 

 rise, the quickly proliferating cocci are not taken up in such numbers by 

 the phagocytes ; the pulmonary alveoli and capillaries thus contain many 

 free cocci, a condition of bactcriaemia results, and with an aggravation of 

 this condition intense intoxication and death. 



In the case of empyaema developing from pneumococcal pleuritis, the 

 numerous cocci present and proliferating between the layers of pleura 

 absorb all the opsonin from the exudate effused. On opening such a 

 pleural cavity fresh serum laden with opsonin is poured out into the 

 cavity, the cocci are taken up rapidly by the leucocytes in the granulating 

 zone and exudate and destroyed. The condition, therefore, tends to go 

 on to healing should the opsonic content of the serum be sufficiently 

 high. If it be low, it is manifest that the serum poured into the opened 

 pleural cavity would also be low, the cocci would be less efficiently 

 picked up by the leucocytes, and the disease would tend to continue for 

 a longer period and become an essentially chronic discharging empyaema. 



Analogous cases are tuberculous and staphylococcic abscesses, in 

 which, as Wright and Bulloch have demonstrated, the fluid of the pus of 

 a closed abscess possesses no opsonic power, although the blood of the 

 patient exhibits it in a considerable measure. If these be opened, the 

 lymph afterwards flowing from the wound has high opsonic power. 



(379) 



