The Washed Leukocytes 277 



and counterstained with methylene-blue, or perhaps better with 

 gentian violet and counterstained with Bismarck brown or vesuvin. 



The final step in the process is the enumeration of the bacteria 

 in the corpuscles by averaging the number taken up by the cells. 

 Only typical polymorphonuclear cells should be selected for staph- 

 ylococcic cases, and separate averages made for polymorphonu- 

 clear and mononuclear cells in tubercle bacillus cases. It is best to 

 follow certain routine methods of enumeration. Some who content 

 themselves with a count of the number of bacteria in 20 ceDs, 

 secure less accurate results than those who count 50 cells. It is 

 usually best to count one-third of the cells in the central portion 

 of the spread, one-third at the edge, and one-third at the end. 

 In each portion no other selection of cells should be made than the 

 elimination of other than polymorphonuclear cells and the elimina- 

 tion of all crushed or injured cells; the others should be taken one 

 after the other, as they are brought into the field with the mechanical 

 stage. After the bacteria included in each of the accepted number 

 of cells selected as the standard has been enumerated, an average 

 is struck. 



The "opsonic index" is determined by dividing the average 

 number in the patient's serum preparation by the average in the 

 normal serum preparation. 



Leishman's* studies of the phagocytic power of the blood show 

 that in cases of furunculosis, etc., with each recrudescence of boils, 

 there is a marked diminution of the phagocytic power of the blood, 

 and with each improvement, a marked increase. 



McFarland and I'Englef found by an examination of the blood 

 of 24 supposedly healthy students and laboratory workers that it 

 was possible to prejudge, by the phagocytic activity of the cells, 

 the past occurrence of suppuration- and present liability to it. 



Wright and Douglas use the opsonic index as a guide to the 

 specific therapy of the infectious diseases. If the opsonic index is 

 low they believe bacterio-vaccination is indicated. In its admin- 

 istration, however, care must be taken to administer a counted 

 number of bacteria, and to make frequent opsonic estimations to 

 determine the good or ill effects accomplished. Thus, the ad- 

 ministration is always followed by a temporary diminution (negative 

 phase) of the opsonic index, soon followed, if the dose be not too 

 large, by a marked increase (positive phase). It is supposed, 

 upon theoretic grounds, and proved by practical experience, that 

 the increase of phagocytic activity brings about improvement. 

 The care of the operator should be to avoid giving so large a dose of 

 the vaccine that the negative phase will be so long continued that 

 harm instead of good may be achieved. 



Although Wright is said to cling to the study of the opsonic 



* "Lancet," 1902, i, p. 73. 

 t "Medicine," April, 1906. 



