24 VACCINE AND SERUM THERAPY. 



is a substance present in all serum. The amount varies in the 

 different sera and as the amount varies so also will the amount of 

 phagocytosis vary. To determine the phagocytic power it is 

 necessary to have the three factors of phagocytosis in the mix- 

 ture. These three factors are found in the blood serum, leuco- 

 cytes and bacteria. A mixture of these three must be allowed 

 to remain together for a definite period of time, after which the 

 average number of bacteria taken up by the polymorphonuclear 

 neutrophiles must be determined. This average number of bac- 

 teria per leucocyte is called the "phagocytic index." The 

 phagocytic index obtained when serum from the patient is mi^ed 

 and incubated with leucocytes and bacteria, is compared with 

 the phagocytic index obtained when serum from a healthy in- 

 dividual is added to and incubated with a similar amount of the 

 same emulsions of bacteria and leucocytes. The result obtained 

 is called the "opsonic index." 



The technique here given is essentially the one developed 

 by Wright and Douglas and demonstrated in New York City in 

 1906 by Wright and taught by his associate, Dr. Ross. It is 

 given somewhat in detail inasmuch as it is the one most generally 

 used, even though many modifications have been suggested and 

 followed by different investigators. 



SERUM. 



Blood from the individual whose serum is to be used in the 

 determinations of the opsonic index, is collected as follows: A 

 small glass capsule with one curved capillary limb is made as is 

 indicated in Fig. 4. This tube is brought to a needle's point at 

 "b" by heating over the pilot flame of a Bunsen burner. This 



FIG. 4. 



point is later used to puncture the finger or lobe of the ear. The 

 end "a" of the capsule is left open. One of the fingers of the 



