284 AMBOCEPTOR AND OPSONIN 



phagocytosis than are normal ones, but the difference is not great. 

 They are, however, much more easily opsonized by normal serum, 

 or by serum that has had its amboceptor removed by treatment 

 with staphylococci in the cold. 



In other cases the conditions are more complex, for when a 

 potent bacteriolytic serum is present, bacteriolysis may occur to 

 such an extent as to diminish . the number of organisms which 

 can be taken up by the leucocytes. We then get the " reversed 

 ratio " phenomenon described by Leishman and Dean. It is as 

 follows : Under ordinary conditions the index falls greatly on 

 heating, as has been shown. This is called the normal ratio. 

 But in some of the potent sera obtained from highly immunized 

 animals the opsoni^ index may apparently rise after heating to 

 two or three times that of the raw serum. This Dean explains 

 and his explanation is an extremely rational one by invoking 

 the bacteriolytic action of the unheated serum. The number of 

 bacteria in the emulsion is reduced, so that there are fewer for the 

 leucocyte to take up ; some that are not completely dissolved 

 may lose their power of retaining stains and become invisible ; 

 bacteria partially acted on may be readily digested within the 

 leucocyte, so that they are not counted ; and, lastly, the dissolved 

 bacteria may have a toxic effect on the leucocytes. The 

 phenomenon of the reversed ratio may be taken as an argument 

 in favour of the equivalence of thermostable opsonin and 

 amboceptor. 



The strongest argument, however, is derived from the experi- 

 ments of Dean, who has shown that in different samples of 

 immune sera there is a distinct parallelism between the two 

 functions : when the serum is powerful as a bacteriolytic agent, 

 when activated with a suitable complement, it is also powerful as 

 an opsonin after heating. It must be admitted, of course, that a 

 serum may be opsonic, but not bacteriolytic ; but this is explicable 

 on the assumption that much less of the substance is required to 

 sensitize the bacterium to the attack of leucocytes than is necessary 

 to render it soluble by complement. This has been confirmed 

 by Neufeld and Bickel, who found that a very minute amount of 

 haemolytic serum, far less than would produce haemolysis, would 

 act as a haemopsonin. 



The opsonic index does not rise pan passu with the bacteriolytic 

 power, but this is partly due to the fact that the criteria are 



