OPSONIC METHODS 123 



simple method, as follows : A piece of quill tubing is drawn out 

 to a capillary diameter so as to make a pipette about 6 inches 

 long. The point is broken off, and a rubber nipple adjusted to 

 the wide end ; a mark is made with an oil pencil about three- 

 quarters of an inch above the orifice. Blood is drawn from the 

 finger up to the mark, then an air-bubble is allowed to pass in. 

 A thin emulsion of the bacterium to be tested having been pre- 

 pared, a quantity of this is also drawn up to the mark. The 

 two fluids are thoroughly mixed by being first blown out on 

 to a sterile slide and then drawn back into the pipette and 

 expelled, this being repeated several times. A cover-glass is 

 placed over the drop, and the slide is placed in the incubator 

 at 37 C. for fifteen minutes. The cover-glass is then slipped 

 off so as to make a film preparation, which in the case of 

 ordinary bacteria may be stained by Leishman's method. The 

 number of bacteria present in, say, fifty polymorphonuclear cells 

 successively examined is determined, and an average struck. The 

 method was first used for showing that in cases of staphylococcus 

 infection the average number of bacteria taken up was less than 

 in a control in which the same bacterial emulsion was exposed 

 to the blood of a healthy individual. In making such an 

 observation, drops from the two mixtures are placed on the same 

 slide under separate cover-glasses, and the preparation incubated. 

 One cover is slipped to one end of the slide, and the other to 

 the other, the two films being then stained as one. 



Irishman's method gives what may be called the total phago- 

 cytic capacity of the blood, but according to Wright's view the 

 process of phagocytosis in blood outside the body is not a 

 simple one, and before a leucocyte takes up a bacterium the 

 latter must be acted on in some way by substances present in 

 the serum, which Wright calls opsonins (see Immunity). The 

 technique by which the actions of these opsonins is studied 

 has been elaborated by Wright and his co-workers in connection 

 with bacterial vaccines, especially in relation to infection by the 

 pyogenic cocci and the tubercle bacillus. The method can be 

 applied in a great many other infections, though difficulties arise 

 with certain bacteria, e.g., b. influenzas, b. mallei, certain pseudo- 

 diphtheria bacilli, on account of the difficulty of recognising these 

 when lying in the protoplasm of the phagocyte. The technique 

 involves (1) the preparation of the bacterial emulsion, (2) the 

 preparation of the leucocytes, (3) the preparation of samples of 

 (a) serum from a normal person, and (b) serum from the infected 

 person. 



(1) Preparation of Bacterial Emulsion. In the case of 



