DETERMINATION OF OPSONIC INDEX 2OQ 



polymorphonuclear leucocytes are now examined and the number of 

 microbes they contain enumerated. 



Similar calculation is undertaken with the normal control serum. The 

 fraction obtained by dividing the number of bacteria contained in 100 cells 

 on the patient's slide, by the number in 100 cells on the normal slide, gives 

 the opsonic index of the patient's serum. 



For example, the normal individual has 284 and the patient 262 bacteria 

 in 100 cells, the fraction which gives the patient's opsonic index would be 

 262/284 r 0.92. 



The principle of Wright's technique is simple, but it requires a great 

 deal of practice before it is mastered. Only then are the results reliable. 

 One must adopt the same principles when counting the control slide as 

 when the patient's film is counted. If in the last case, for instance, the 

 cocci situated on the edges of the cells are not included in the count, 

 they should also be excluded in the first case. The absolute count is of no 

 importance. It is the relative proportion which is significant. 



As a normal control, it is best to take the average of the phagocytic 

 counts of a series (3 to 4) of normal sera or first equally mix the different 

 sera, and take the phagocytic count of the pool. 



Normal sera should not differ from one another in a tubercular opsonic 

 estimation by more than 10 per cent. 



Wright's Vaccine Treatment. 



As has been said, the principle of Wright's vaccine treatment depends 

 upon the immunization with small doses of dead bacteria, so-called vac- 

 cines, whereby the opsonic index of the individual is raised. This is usu- 

 ally associated clinically, with improvement in the patient's condition. 



The effect of the immunization according to Wright depends upon: 



1. Individual reaction of the patient. 



2. Preparation of the vaccine. 



3. Dosage and form of application. 



The individual reaction of the patient can be measured by the opsonic 

 index. 



As far as the preparation of the vaccine is concerned, Pasteur's conten- 

 tion that a vaccine must necessarily be made up of living cultures has 

 not proved itself correct. Carefully killed cultures suffice in almost all 

 cases. An example of the preparation of Wright's vaccine is here given. 



The Preparation of a Staphylococcus Vaccine. 



Agar cultures are grown for twenty-four hours, and about 3 c.cm. of 

 sterile normal saline solution are added to each culture. The growth is 

 washed off in the saline solution by means of a platinum needle or freshly 



14 



