GO INFECTION, PHAGOCYTOSIS, OPSONINS 



formed. This is drawn off with a pipette and the centrifuge tube is 

 now filled by pouring into it a 0.85 per cent, (physiologic) salt solution. 

 The tube is shaken so that the sediment is thoroughly mixed with 

 the salt solution and again centrifuged. The clear upper stratum is 

 once more drawn off and the sediment is once again shaken with the 

 salt solution. After a final centrifuging the tube will present three 

 layers: a lowest scarlet sediment of red blood corpuscles, a narrow 

 grayish-red ring which contains the leukocytes, and a perfectly clear 

 top layer which is the salt solution. The latter is very carefully drawn 

 off with a pipette with rubber bulb, so that the gray ring of leukocyte 

 is not disturbed. After the salt solution has been drawn off the 

 grayish layer is carefully drawn into a small pipette and at once 

 expelled into a watch-glass, which is covered to prevent evaporation. 

 The watch-glass now contains a mixture composed of salt solution, 

 suspended leukocytes, and also a few red blood corpuscles. Their 

 presence, however, does not interfere with the use of the suspension 

 or emulsion of washed leukocytes. When these are to be employed 

 either in experimental work or in order to ascertain the opsonic index 

 (see below), a small amount of the suspension is drawn into a fine 

 glass pipette. If a little air bubble is now drawn up and then an 

 amount of bacterial emulsion, equal to the leukocyte emulsion, these 

 two fluids can be mixed in the pipette by repeatedly drawing them up 

 and expelling them on a clean slide. After they have been finally 

 drawn into the pipette the point of the latter is sealed in a flame, 

 and the pipette and its contents can now be placed in an ordinary 

 bacterial incubator or into a so-called opsonic incubator. The 

 mixture is generally left in the incubator for one-half hour; then 

 the pipette is removed, its sealed point broken off, and the contents 

 blown onto a clean slide. The drop is then spread with the margin 

 of another clean slide, the preparation is air dried, fixed in the flame 

 or in alcohol, and stained. It can now be examined with the oil- 

 immersion lens of the microscope like any other bacterial prepara- 

 tion. If the test has been made as described above, it will be found 

 on microscopic examination that very little if any phagocytosis has 

 occurred. 



Opsonins. It has been found by Wright and Douglass that the 

 blood serum contains certain substances which so prepare bacteria 

 that they are subsequently taken up by phagocytes with avidity. 

 These substances contained in the blood serum have been called 

 opsonins (a . word derived from a Greek verb which means to 

 prepare). 



Characteristics. It is not known definitely what these substances 

 are. Some investigators strongly maintain that they are identical 

 with hemolytic and bacteriolytic amboceptors (see below). Other 

 serum investigators claim that they are bodies, sui generis, and not 

 identical with any of the other antibodies. Be this as it may, it has 

 been shown beyond a doubt that the blood serum contains certain 



