240 



OPSONINS 



on every occasion. The reaction is much more reliable in the " surgical 



tuberculoses" than in pulmonary tuberculosis. 



In suspected cases of enteric fever an opsonic index above 1*7 for the 



typhoid bacillus affords strong presumptive evidence in favour of enteric 



fever (Milhit). Similarly in cerebro-spinal meningitis the opsonic index is 



raised above normal during the 

 course of the disease ; and so on. 



Method of determining the opsonic 

 index. 



The following materials and appa- 

 ratus are necessary : 



Apparatus. Small test-tubes 

 Pasteur pipettes fitted with india- 

 rubber teats, these should be made 

 from tubing 4-5 mm. in diameter 

 and be drawn out rather long (fig. 

 162). Bulb pipettes fitted with a 

 small india-rubber aspirating tube. 

 A mechanical centrifuge. An 

 Hearson's opsonic incubator (fig. 

 161) heated by gas or electricity 



FIG. 161. Opsonic incubator. an( J re gulated at 37 C. 



A supply of sterile normal saline solution and of citrated saline solution 

 must be at hand : 



Sodium chloride, - 8 '5 grams. 



Sodium citrate, - 15 



Distilled water, - - Q.S. ad 1 litre. 



Normal serum. Collect some blood in a small centrifuge tube either from 

 an animal by puncture of an ear vein or from man by pricking the finger. 

 (Chap. XII.). Centrifuge the blood at once and decant the serum with a 

 Pasteur pipette. The serum is best collected when the individual is fasting 

 (Milhit) : it should be used as soon as possible and always within 2 or 3 hours 

 of collection because the opsonic power rapidly diminishes. 



Patient's serum. This should be collected under the same conditions and at the 

 same time as the normal serum in order that the results may be comparable. 



Bacterial emulsion. [When the rate of growth permits] very young 

 cultures should be used (8-24 hours old according to the organism), and for 

 the same series of experiments cultures of the same age and prepared under 

 identical conditions are necessary. 



As a rule, agar cultures are used and one loopful is made into an emulsion 

 with 2 c.c. of normal saline solution. The emulsion must be carefully pre- 

 pared ; it should be slightly opalescent when held up to the light and must 

 be perfectly homogeneous. If too thick an emulsion be used it will be difficult 

 to enumerate the organisms in the subsequent part of the experiment. 



Leucocytes. 1. Cleanse the skin of the thumb, tie an india-rubber ligature 

 around its proximal end and then make several little pricks on the dorsal 

 surface of the distal end near the root of the nail. 



2. Allow about thirty drops of blood to flow into a small sterile centrifuge 

 tube containing about 10 c.c. of citrated normal saline solution (fig. 147, p. 192). 



3. Mix the blood and citrate solution carefully, centrifuge the mixture for 

 15 minutes, decant the supernatant liquid with a bulb pipette, add an equal 

 volume of normal saline solution to the deposit, mix and centrifuge again. 

 Then decant the saline solution and wash a second time. 



