88 ESSENTIALS OF BACTERIOLOGY 



is sucked up to a certain mark, and, with an air-bubble between, 

 a diluted suspension of bacterial culture is measured into the 

 same tube. From this mixture, one drop is blown out on to a 

 slide and stained according to Leishman's method, and the 

 bacteria compared to the blood-cells. If the observer's blood 

 contained 5,000,000 red cells in a cubic millimeter, and with a 

 i : 3 dilution of the bacteria, the bacteria are equal in number 

 to the red cells, in the undiluted culture each cubic millimeter 

 would contain 15,000,000 bacterial cells. 



Method of Measuring Phagocytosis the Opsonic Tech- 

 nic. First, Preparation of Bacterial Emulsion. The culture 



Fig. 46. Diagram of phagocytosis. Staphylococci in polynuclear leuko- 

 cytes. 



from an agar slant is rubbed in a watch-crystal with 0.85 per 

 cent, saline solution, and the mixture centrifugalized to sedi- 

 ment any masses undissolved. The emulsion should then be 

 just very slightly cloudy, and will contain about 10,000,000,000 

 bacteria per cubic centimeter. 



Second, Preparation of Leukocytes. Healthy blood-cells are 

 used preferably the observer's. At least ten drops of blood 

 are mixed in a test-tube containing 3 c.c. warm normal salt 

 solution, to which 1.5 per cent, sodium citrate has been added; 

 this is then centrifuged, the supernatant fluid removed down 

 to the layer of leukocytes, and an equal quantity of normal salt 



