TUBERCULOSIS OF THE EYE 355 



normal. This is especially the case for an immunized animal. Immune serum 

 taken from such an animal, on account of its opsonin contents, has the power of 

 raising the opsonic power of another individaal, thus causing a passive immunity. 

 Similarly the body will itself actively form opsonin when small doses of dead 

 bacteria are introduced into it. 



The new tuberculin (Koch) contains broken-up and dead tubercle bacilli. 



If a small dose be injected, the phagocytic power is reduced by the poison intro- 

 duced, as is the case for all injections of this kind, and a negative opsonic phase 

 begins. This will be followed by an increase in the formation of opsonin, pro- 

 vided that the infection be not too severe. The phagocytic activity the opsonic 

 power increases, and the conditions are in general more favourable for the healing 

 of the local affection in question. 



Wright lays special importance on the hypothesis that no new injection should 

 take place during the negative phase or period in which the opsonic power is 

 sinking, otherwise this power may be successively reduced. Only during the 

 positive phase is a new dose to be injected, and the amount should be regulated 

 according to the ' opsonic index.' 



The term ' opsonic index ' is used by Wright to mean the proportion between the 

 opsonic power of the individual affected and that of a normal man. It is deter- 

 mined in the following manner : ] 



1. Under aseptic precautions some of the blood of the patient is drawn off in 

 a capillary pipette and centrifugalized. The cell-free serum is collected. 



2. Blood is taken from a normal individual, mixed with isotonic 10 per cent, 

 citrate of soda solution to prevent coagulation, freed from serum, and then 

 washed with saline. An equal quantity of the solid elements of the blood (red 

 and white corpuscles) is added to the serum obtained in process (1) from the 

 patient. 



An equal quantity of a dilute suspension of the bacteria to be tested (here the 

 Bac. tuberculosis) is then added. 



The mixture (patient's serum, normal corpuscles, and bacteria) is then placed in 

 the incubator for fifteen to twenty minutes at 37 C. From the mixture evenly- 

 spread smears are made, dried, carefully fixed in the flame, and stained. The 

 polynuclear leucocytes are examined in various fields, and the number of bacteria 

 contained in 60 to 100 of them is determined ; the leucocytes tend to collect at one 

 end of the preparation. The number of these bacteria divided by the number of 

 the cells is the ' phagocytic index.' 



An exactly similar examination is made of the serum of a normal individual, 

 and the phagocytic index then obtained is compared with that of the patient. 



Phagocytic index of the patient _ 0psONIC INDEX 



; ; ^ \sr ow^i !*_ -LJ^i Ltd A. 



irhagocytic index of a normal man 



This opsonic index or opsonic power of the affected person informs us whether 

 the resistance is raised or lowered. The index must be worked out for the individual 

 bacterial strain. All estimations must be made by the same person, so as to reduce 

 the personal factor. 



The ' opsonic power ' can be raised by the various methods of immunizing the 

 injection of immune serum (passive), the injection of bacteria or their toxins 

 (active) which can induce in the body the active formation of antibodies, in this case 

 opsonins. In the discussion of the pneumococcal serum treatment (p. 331) it has 

 been stated that the action here is not a direct bactericidal one, but a ' bacteriotropic ' 

 {Xeufeld and Eimpau). This view corresponds to a great extent with the ' opsonic ' 



1 For further details, see the publications of Wright and his pupils. 



232 



