OPSONIC INDEX AND VACCINE THERAPY 329 



Yet the controversy between the strictly humoral and the cellular 

 schools was by no means regarded as closed, especially since, in such 

 cases as typhoid infection, the parallelism between increased resist- 

 ance and extracellular bactericidal power was so plainly evident, 

 while in this disease particularly (for technical reasons which will 

 become clear as we proceed) no such parallelism with phagocytosis 

 could at first be shown. It was because of such apparent confusion 

 that Leishmann 5 undertook to study again the relation of phago- 

 cytosis to active immunity, chiefly upon staphylococcus cases that 

 were being "vaccinated" therapeutically by Wright himself. 



In order to obtain a numerical measure of the degree of phago- 

 cytosis, he developed a simple technique which, though crude, served 

 to give him the information he sought. It consisted in taking small 

 quantities of the blood of patients and mixing these in capillary 

 pipettes with equal volumes of bacteria suspended in salt solution. 



The mixtures were then placed on slides, covered with a cover- 

 slip, and incubated at 37 C. for varying periods. At the end of 

 incubation the preparations were smeared upon slides and stained 

 by Leishmann's modification of the Romanowski method, the num- 

 ber of bacteria in a large series of leukocytes counted and an average 

 taken. 



This method had many serious flaws, chief among them being 

 the liability to coagulation of the preparations and the fact that, in 

 each test, the fluid constituents as well as phagocytes, both of them 

 variable factors, came from -the same individual. While, therefore, 

 it was possible to estimate an increase or decrease of general phago- 

 cytic power, it was impossible to analyze this in reference to its de- 

 pendence either upon the condition of the cells, on the one hand, or 

 that of the plasma or serum, on the other. Moreover the relation of 

 the number of leukocytes to that of bacteria in individual tests neces- 

 sarily differed, and this, we have seen, adds a variable factor which 

 renders it impossible to compare any two experiments with accuracy. 



In spite of these difficulties, however, Leishmann succeeded in 

 establishing, in a number of cases of staphylococcus infection, that 

 an increased resistance was accompanied by an increased energy of 

 phagocytosis. 



Leishmann, however, went no further than this, and interpreted 

 his results on the basis of the "stimulin" theory of Metchnikoff. 



The subsequent studies of Wright, which began at the point at 

 which Leishmann stopped, have been described in the preceding chap- 

 ter and had, as their main result, we have seen, the discovery of the 

 opsonins and the final confirmation of Denys' conception of the true 

 mechanism of cooperation between serum and leukocytes in phago- 

 cytosis. In order to carry out these studies the technique of Leish- 



5 Leishmann. Br. Med. Jour., 1, 1902 ; Transact. Lond. Path. Soc., Vol. 

 56, 1905. 



