390 



EXPERIMENTAL INFECTIONS DURING LIFE 



a platinum spatula, transferring it to an agate mortar 

 and grinding it up with successive small quantities of 

 normal saline. If satisfactory insert the tube in the 

 plasticine block next to that containing the washed cells. 



Specific Serum. 

 Pooled Serum. 



These sera are collected and treat- 

 ed as already described (see page 

 379), and the portions of the blood 

 pipettes containing them are ar- 

 t_, F I G ' - 1 , 94 ' P1 ^ icine ranged in the remaining space in 



block with materials ar- . 



ranged for opsonin esti- plasticine block. 



The plasticine block now presents 

 the appearances shown in Fig. 194. 



METHOD FOR DETERMINING THE OPSONIC INDEX. 



1. Take a capillary pipette fitted with a teat, cut the 

 distal end square and make a pencil mark about 2 cm. 

 from the end. 



2. Aspirate into the pipette one volume of washed 

 cells, air index, one volume of bacterial emulsion, air 

 index, and one volume of specific serum (see Fig. 195). 



Serum 



Bacterial Washed cells 

 emulsion 



FIG. 195. Opsonin pipette. 



3. Mix thoroughly on a 3 by i slide by compressing 

 the teat and ejecting the contents of the pipette on 

 to the surface of the slide, relaxing the pressure and 

 so drawing the fluid up into the pipette again. These 

 two processes should be repeated several times ; finally 

 take up the mixture in an unbroken column to the cen- 

 tral portion of the capillary stem. 



4. Seal the point of the pipette in the peep flame of 

 the bunsen burner and remove teat. 



