470 H^EMOLYSINS AND ALLIED BODIES 



leucocytes when a bacterial suspension is mixed with a suspension 

 of washed leucocytes. 



Something must therefore be contained in normal blood serum 

 which renders bacteria susceptible of being absorbed by leucocytes. 



This substance they have named an opsonin (feast preparer). 



By heating the normal serum to 60 or 65 C. for fifteen 



minutes its opsonin is destroyed, and it is now no longer capable 



. of sensitising bacteria towards leucocytes. 1 If, on the other hand, 



the bacteria be first of all incubated at 37 C. with normal serum 



and then heated to 60 or 65 C. they remain sensitised. 



These experiments recall much of what has been described in 

 connection with Ehrlich's side-chain theory. The opsonin probably 

 possesses a haptophoric group whereby it unites with the bacterium, 

 and an activating group, whereby it produces some chemical or 

 other change in the leucocyte which stimulates the latter to 

 absorb the bacterium. The activating group can produce this 

 effect on the leucocytes only after the haptophoric group has 

 become fixed to the receptor of a bacterium. The one group is 

 like the haptophoric group of a complement, the other like the 

 acting group, and this analogy to the complement is further sus- 

 tained by the instability of opsonins to heat. 



The opsonins in the blood serum of one species may sensitise 

 bacteria towards the leucocytes of a different species. 



Dead bacteria can absorb opsonins, for, if serum be digested with 

 these it can no longer sensitise living bacteria ; the receptor group 

 of the bacterium therefore still remains capable of joining with 

 the haptophoric group of the opsonin after the bacterium is dead. 



In some interesting experiments recorded by Bulloch and 

 Atkin ( 19 ) it is shown that all healthy leucocytes possess an equal 

 phagocytic power, provided they be brought in contact with 

 the same bacteria sensitised by the same opsonin. If, on the 

 other hand, different opsonins be used to sensitise the same 

 bacteria, and these latter be brought into contact with the same 

 leucocytes, the number of bacteria picked up by each leucocyte 

 will be found variable. Opsonins from different individuals possess 

 different sensitising powers. Of great significance is one result 

 obtained by Bulloch and Atkin showing that the blood serum 

 of a girl suffering from facial lupus and tubercular sores on the 



1 The heat destroys the amount of opsonin present in normal serum (as tested 

 by Wright's method). A patient infected with tuberculosis has opsonin in his 

 blood which is not all destroyed by heat in 15'. By this simple test cases of 

 tuberculosis can be diagnosed (Wright). The injection of nuclein increases the 

 quantity of opsonin (Bulloch). (Editor's Note.) 



