272 



The Phagocytic Power of the Blood 



culated. It requires experience to determine the appropriate number 

 of bacteria to be employed. When this is once determined, future 

 manipulations are made easy, because one first makes his suspension, 



Fig. 94. — Photomicrograph showing cross-hairs, bacteria, and red blood- 

 corpuscles (Miller). 



then enumerates the bacteria, and having determined their number, 

 immediately arrives at the appropriate concentration by dilution. 



Fig. 95. — Collecting blood for corpuscles (Miller). 



The Washed Leukocytes. — It is not necessary to have the leuko- 

 cytes free from admixture with the erythrocytes, but it is necessary 

 to have large numbers of them. They are collected by citrating the 

 blood so as to prevent coagulation, and then separating the citrated 

 plasma from the corpuscles by centrifugalization. 



