204 



PHAGOCYTOSIS. OPSONINS AND BACTERIOTROPINS 



allowed to cool; by the cooling the blood is sucked back from the 

 unsealed capillary end; this end may also be sealed in the tip of the 

 flame. The blood then coagulates and the serum separates off. The 

 separation of the latter may be hastened by centrifugalization for a 

 short time. 



FIG. i 8. 



FIG. 19. 



FIG. 20. 



In order to obtain leucocytes, a small test-tube which holds 3 to 4 c.cm. 

 is filled 2/3 with a 1.5 per cent, solution of sodium citrate, and about 6 

 to 7 drops of blood from a healthy individual" are collected in .this 

 solution (Fig. 21). The tube is inverted several times to thoroughly m 



FIG. 21. 



FIG. 22. 



the blood so that the citrate, by precipitating the calcium salts of the 

 blood, effectively prevents coagulation. The suspension is centrifugalized 

 until the corpuscles are thrown down and a distinct white layer (leucocytes) 

 is seen upon the surface of the red cells (Fig. 22). The clear supernatant 

 citrate solution is pipetted off, care being taken not to disturb the white 

 layer. Some 0.85 per cent, saline is added, mixed and the mixture again 



