IMMUNITY IN PNEUMOCOCCAL INFECTIONS 27 



Similar experiments on immune sera from various sources gave a 

 similar result, though the amount of thermostable element varied. greatly 

 in quantity. It is not proportional to the amount of opsonin present, or 

 to the opsonic index. 



The opsonic indices of two individuals may be the same, though one 

 has been subjected to active immunisation. Both may be unity, yet, 

 when subjected to heat, the difference between the two becomes 

 apparent. 



Example:— Cocci per 



leucocyte. 



Immune serum -------- n-g 



Normal serum -------- 8*8 



Heated immune serum - 3-2 



Heated normal serum - - - - - - - . i-i 



Supernatant fluid after digestion — immune - - - 3-4 

 i» II — normal - - - o'8 



Normal corps. + deposit from "immune ".digestion - 2*0 

 II + II " normal " digestion - - 2*1 



It would appear, therefore, that the serum of an individual which has 

 been raised artificially to the normal standard differs considerably as 

 regards thermolability from that of a normal individual. 



With regard to the nature of the residual body after heating, it is 

 present in the serum, not destroyed by heat, it does not attach itself to 

 fresh bacteria added, and yet it causes phagocytosis. Most probably it 

 acts as a stimulant to the leucocytic amoeboid movement — a true 

 stimulin. 



In the active immunisation of animals, this residual substance appears 

 previous to the increase in opsonic index, and disappears for a short time 

 before the opsonic index has again fallen to unity. 



Relation of the Opsonin to the Leucocytosis. — In the examination of 

 typical cases of acute croupous pneumonia, it would appear as if the 

 leucocytosis curve and that of the opsonic content were inversely 

 proportional, and this is so close that prima facie one might be led to 

 trace phenomena of cause and effect, either that the rise in opsonic 

 content caused the fall in the number of leucocytes or vice versa. 

 The best method of determining whether any causal nexus exists between 

 the two factors is by animal experiment. Thus, a rabbit was inoculated 



(391) 



