330 INFECTION AND RESISTANCE 



mann was quite inadequate, and Wright's first task was to modify it 



in such a way that reasonably accurate comparative estimates of 



phagocytosis could be made. 



It is necessary to outline Wright's method briefly in this place 



in order that we may consider possible sources of error and obtain 



a clear understanding of the conclu- 

 sions he based on his observations. 

 Wright recognized that the deter- 

 mination of the degree of phago- 

 cytosis, induced by the opsonin of 



any given serum in a single test, is 

 WRIGHT CAPSULE FOR TAKING , J ., fe -. ,, ,, , . -, 



BLOOD TO OBTAIN SERUM FOR by itself of no value, since the actual 



OPSONIC TESTS. number of bacteria taken up by each 



leukocyte, apart from the opsonic 



contents of the serum, depends also upon such purely technical fac- 

 tors as the concentration of the bacterial emulsion, the relative num- 

 ber of leukocytes, and the length of time of incubation. Two 

 individual tests, therefore, carried out with the serum of the same 

 patient at the same or at different times, with different bacterial 

 emulsions or leukocytes in each, 

 would give variable results, even 

 though the opsonin contents them- 

 selves were entirely alike. 



In order, therefore, to obtain 

 a relative estimate of the opsonic 

 contents of any serum it is neces- 

 sary to compare the phagocytic ac- 

 tivity induced by this serum with 

 the similar power of another sup- 

 posedly normal serum, both tests 

 being carried out, under exactly 

 similar conditions, with the same 

 bacterial emulsion and the same 

 leukocytes. The average number 

 of bacteria found in each leuko- |fj 



cyte in each one of the prepara- 

 tions is then the a phagocytic in- ^^~ - 

 dex." The relation of the phago- ^- mm 



cytic index of the unknown serum METHOD OF PRODUCING AN EVEN 

 to that of the supposedly normal EMULSION or BACTERIA FOR Op- 

 serum constitutes what Wright has SONIN DETERMINATION. 

 called the "opsonic index." 



Instead of using the whole blood of the patient Wright takes a 

 small amount of blood in glass capsules, allows it to clot, and uses 

 the expressed serum in his test. For comparison with this he em- 

 ploys a "pool" of a number of specimens of serum from supposedly 



