PHAGOCYTOSIS 261 



We see in this case that the patient's blood has but half the 

 opsonic power of normal blood ; this we express by saying that 

 the opsonic index is 0-5. The opsonic index is obtained by dividing 

 the number of bacteria found in a certain number of leucocytes 

 in the films made with the patient's serum by the number of 

 bacteria in the same number of leucocytes in the films with the 

 control serum, and expresses the phagocytic power of the patient's 

 serum as compared with that of a healthy person. It is not 

 necessarily an exact measure of the amount of opsonin, since on 

 dilution of a serum the opsonic index falls at first slowly and then 

 more quickly, forming a flat-topped curve when plotted out in the 

 usual way (see Fig. 59, p. 265). 



Other methods for the estimation of the opsonic index have 

 been suggested, and require some mention. In the earliest 

 method that of Leishman the patient's blood was mixed 

 directly with an emulsion of the bacteria in normal saline solution 

 in equal parts, and a drop of the admixture placed on a slide, 

 covered with a cover-glass, and incubated for a definite time. A 

 control specimen was prepared in a similar way, using normal 

 blood. After the incubation, films were prepared by sliding the 

 cover-glass off the slide, stained, and a count made as in the 

 method now in use. A similar but rather better method is also 

 employed, and is extremely convenient in some cases. The 

 bacterial emulsion is prepared as above, the organisms being 

 suspended in normal saline solution containing sodium citrate. 

 A mixture of this emulsion and of the patient's blood in definite 

 amounts (usually equal parts) is prepared, sucked into the pipette 

 (the tip of which is sealed), and incubated for a quarter of an 

 hour or twenty minutes. The process is the same as Leishman's 

 except that the mixture is incubated in a pipette, and not between 

 slide and cover-glass. A control is also prepared, using the same 

 emulsion and normal blood, and is also incubated for a quarter 

 of an hour. At the end of this period films are prepared, and 

 the process finished in the ordinary way. 



This method is theoretically more accurate as a test of the 

 phagocytic activity of the patient's blood as compared with normal 

 blood than is the opsonic index as determined in the ordinary 

 way, in which leucocytes from the same source are used in both 

 determinations *'.., in that of the patient's serum and in that 

 of the control. Thus, if in any case the leucocytes were so 

 injured that they had very little phagocytic power, the opsonic 



