266 



MEDICAL BACTERIOLOGY 



The contents of the tube are then thoroughly mixed by ejecting them into a 

 sterile watch crystal and drawing them back into the tube several times. When 

 mixed the fluid is drawn to the middle of the tube, the ends sealed and an identi- 

 fication mark placed on the tube. The tube is then incubated at body tempera- 

 ture for 15 minutes in an incubator that will permit fre- 

 quent rotation of the tube as this is necessary (see Fig. 45). 

 At the same time that blood is drawn from the pa- 

 tient to obtain serum, blood is also collected for the same 

 purpose from several healthy persons and the normal sera 

 is pooled (mixed). 



A second mixing pipette is loaded with equal volumes 

 of cells, bacteria and pooled serum and treated exactly 

 the same as the tubes containing patient's serum. 



When the period of incubation is up, the tube contain- 

 ing patient's serum is emptied on a clean slide, one drop of 

 the fluid is transferred to each of several other slides and 

 these drops are spread in a thin film. 



The slides are fixed and stained. Staining with Leish- 

 man's blood stain is the common method but primary 

 fixation with methyl alcohol for i minute followed by 

 staining with dilute fuchsin for a minute gives a more dis- 

 tinct field. The slides so prepared are examined with the 

 oil immersion lens. The number of bacteria within each 

 leucocyte is recorded and when 100 leucocytes have been 

 examined the average number of bacteria per leucocyte 

 is computed; this number is the patient's opsonic content. 

 By examining in the same way the contents of the 

 second tube the normal opsonic content is determined. 



The patient's opsonic content, divided by the normal 

 opsonic content, equals the patient's opsonic index. 



Using this test Wright discovered the following facts. 

 When washed free of blood serum leucotyes almost en- 

 tirely lose their phagocytic power; in other words, there 

 is some substance in blood serum which does not destroy 

 bacteria but acts on them so as to facilitate their ingestion 

 and digestion by leucocytes; to this substance he gave 

 the name opsonin. The quantity of potency of opsonin 

 varies; it is low when immunity is slight and high when 

 immunity is strong. There is natural opsonin that 

 which is present throughout life regardless of infection and acquired 

 opsonin, developed as a result of infection or vaccination. 



There may be both thermolabile and thermostabile opsonins present at the 

 same time in a given animal's serum. 



Opsonin seems to be entirely specific in nature in an animal it may be 

 below normal for one organism and normal for other organisms; in vitro, the 



Mar 



Leucocytes 



Air bubble 

 Bacilli 



Air bubble 

 Serum 



FIG. 45. (Citron.} 



