PHAGOCYTOSIS 27! 



specific, and that any immunity due to them would be a general 

 one. 



The second method is by a comparison of various sera in their 

 action on various organisms. For example, we may take two 

 sera, and compare them in their action on tubercle bacilli and on 

 staphylococci. If we find uniformly that a serum which is low 

 to one is also low to the other, it will tell strongly against the 

 theory of specificity. This, however, is what we do not find, 

 and it is quite usual to discover that a serum which is very low 

 to the tubercle bacillus as compared with a normal control has 

 a normal index to staphylococci as compared with the same 

 control. Of this there can be no doubt. Further, after the 

 injection of a vaccine composed of the dead bodies of certain 

 organisms, it is usual to find the opsonic index to that organism 

 rise, whereas to others it remains unaltered. This tends very 

 strongly to show that opsonins are specific bodies. 



Quite similar results are seen when the behaviour of the 

 opsonic index to two or more bacteria is followed from day to 

 day in a patient suffering from an infection by one of them. 

 Thus, in a patient who was recovering from a severe furuncle 

 the index to staphylococci and tubercle bacilli was observed, with 

 the result shown in Fig. 64. 



Here we may regard the tubercle opsonin as being normal 

 throughout, the slight variations met with being well within the 

 range of experimental error. The index to staphylococci, on the 

 other hand, ranged between 0*4 and 1*35, and showed a general 

 parallelism with the amelioration in the patient's condition. It is 

 obvious that the two indices are not due to the presence of a 

 single opsonin. 



Reverting to the saturation experiments, we may perhaps 

 explain them as follows : Any opsonin can prepare any bacterium 

 for phagocytosis if it combines with it ; but there are different 

 opsonins, with very different degrees of affinity for different 

 bacteria. 1 Thus we may suppose the tubercle opsonin to have a 

 powerful affinity for the tubercle bacillus, a slight one for the 

 staphylococcus, so that the addition of a few tubercle bacilli will 



1 It now seems fairly clear that the explanation of these experiments is that 

 fixation of complement (which in this case acts as an opsonin) takes place. 

 Normal serum contains an amboceptor ( = thermostable opsonin) to staphylo- 

 cocci, though in small amount ; and this, when combined with staphylococci, 

 will attract all the opsonin to it, the staphylococcus opsonin most powerfully. 



