10 QUATERCENTENARY STUDIES IN PATHOLOGY 



Recently, in examination into the phenomena of the immunity 

 acquired in passing through an attack of croupous pneumonia, I made 

 an investigation into the course of the opsonic content of the serum 

 during this disease and in artificial infections in animals. Fifty-five 

 cases were at my disposal, twenty-five of these being more or less typical 

 cases of acute croupous pneumonia ; nine others were in children with 

 the clinical diagnosis of acute croupous pneumonia, seventeen cases were 

 definitely broncho-pneumonia, and the remaining four were cases of post- 

 pneumonic empyaema from which the pneumococcus was isolated in 

 more or less pure culture. 



The technique employed was that of Wright and Douglas. Three 

 parts of the serum of the patient were added to three parts of my own 

 citrated and washed corpuscles and an emulsion of pneumococci. These 

 were thoroughly mixed and incubated at body temperature for fifteen 

 minutes. Films were then made of the contents of the mixing pipette, 

 dried and stained by Leishman's dye. The number of pneumococci in 

 thirty to fifty polymorphonuclear leucocytes were counted and an 

 average per leucocyte determined. Simultaneously with each experiment 

 a control, or series of controls, was made with the sera of normal healthy 

 individuals. The result is expressed in terms of the "opsonic index," 

 the average number of cocci per polymorphonuclear leucocyte when the 

 serum added is that of a normal individual being regarded as unity, and 

 the opsonic index of the pneumonic patient is expressed in relation to 

 the normal opsonic index of a healthy person. 



The strains of pneumococci used in these experiments were seven in 

 number, being isolated from empyaemata and other pneumococcal 

 conditions, and many of them were employed a few days later in testing 

 the sera of the patient from whom they were isolated. All the strains 

 reacted similarly to variations in the opsonic index. The great essential 

 in the preparation of the pneumococcal emulsions is the securing of 

 homogeneity. One strain of pneumococcus had to be discarded owing 

 to the cocci adhering together in clumps, and was therefore quite unsuit- 

 able for the determination of the average number of cocci in a number of 

 leucocytes. The best means of attaining uniformity is to thoroughly 

 shake up the emulsion and then centrifugalise for a few minutes. The 

 masses and clumps are then deposited and the uniform upper layer of 

 emulsion employed in the tests. The cultures were twenty-four hours 



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