CHAPTER XVIII 



THE PHAGOCYTIC POWER OF THE BLOOD AND 

 THE OPSONIC INDEX. 



FROM the time that Metschnikoff connected the phenomena 

 of phagocytosis with those of immunity until 1902, there 

 was no recognized technic for the observation and com- 

 parison of the bacteria-consuming and bacteria-destroying 

 power of the cells. In 1902 Leishman* suggested the 

 following simple technic: 



A thin suspension of bacteria in normal salt solution is 

 mixed with an equal volume of blood by drawing in and 

 out of a capillary tube, then dropped upon a clean slide, 

 covered carefully, placed in a moist chamber, and incubated 

 at 37 C. for a half hour. The cover is then slipped off 

 carefully, as in making blood-spreads, dried, stained, and 

 the number of bacteria in each of 20 leukocytes counted 

 and averaged. For comparison with the normal the patient's 

 blood and normal blood are simultaneously examined. 



This was greatly improved by Wright and Douglas, f the 

 accuracy of whose methods enabled them to discover the 

 "opsonins, " work out the "opsonic index," and formulate 

 methods by which sufficiently accurate observations could 

 be made for controlling the specific treatment of infectious 

 diseases. 



The opsonic theory teaches that the leukocytes are 

 disinclined to take up bacteria unless they are prepared 

 for consumption or phagocytosis by contact with certain 

 substances in the serum that in some manner modify them. 

 This modifying substance is the opsonin (opsono, I cater to, 

 I prepare for). 



To make a test of the opsonic value of the blood it is 

 necessary to prepare the following : 



A uniform suspension of bacteria. 



A suspension in salt solution of washed leukocytes. 



The serum to be tested. 



A normal serum for comparison. 



* "British Medical Journal," 1902, I, Jan. n, p. 73. 

 t "Proc. Royal Soc. of London," 1904, LXXXII, p. 357. 

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