PHAGOCYTOSIS 



275 



lococci or pneumococci. There is, therefore, one important feature 

 possessed by the opsonins in common with the antibodies : in each 

 case an injection of the specific antigen causes first a diminution 

 and then an increase in the amount present. 



There is, however, an important difference. In the other anti- 

 bodies e.g., in diphtheria antitoxin the amount present in the 

 blood can be raised to a point enormously above that of normal 

 blood by a series of inoculations of suitable doses of toxin at suit- 

 able intervals. Here the effect of repeated injections is a cumu- 

 lative one, the second raising the index above the level which it 



FIG. 66. RESULT OF A SINGLE DOSE OF STAPHYLOCOCCIC VACCINE, 

 SHOWING NEGATIVE PHASE. (Original.) 



reaches after the first, and so on. But in the case of the opsonins 

 to most bacteria there is no such summation of results. An in- 

 jection of tuberculin may raise the opsonic index from 0-5 to 2 or 

 a little higher, but with a second injection it is not possible to 

 start with 2 as a base and raise the index to 3, and so on. The 

 maximum indices are not very much above the normal level. In 

 the case of tubercle it is very unusual to find an index as high as 

 2, whilst with the organisms of suppuration, etc., slightly higher 

 figures may occasionally be found. 1 As we have already shown, 

 this does not prove that the amount of tubercle opsonin present 



1 The highest indices of all are met with in the case of the meningococcus. 

 I have seen them exceed 10 in patients treated with vaccine, and higher 

 figures have been recorded. The explanation of these figures will be given 

 subsequently. 



1 8 2 



