80 IMMUNITY 



Opsonins and Opsonic Index. 



Peculiar substances in blood serum have been called by Wright and Douglass 

 opsonins (Greek: prepare food for). If fresh blood is mixed with an emulsion of 

 some bacteria and then incubated for half an hour, it will then be found that many 

 of the bacteria are within the polymorphonuclear leucocytes. If the serum is 

 washed away from the leucocytes before adding bacteria, none of the latter will 

 be found within the leucocytes. This proves that the serum has some influence 

 on phagocytosis. In order to show that this effect is on the bacteria rather 

 than on the leucocytes, the bacterial suspension may be treated with some serum 

 for half an hour and then washed free from this serum by means of a salt 

 solution in a centrifuge, and then mixed with some serum-free leucocytes; then 

 it will be found that phagocytosis occurs as before. The bacteria have been 

 "sensitized." According to Wright this action is comparable to cooking. 



Phagocytosis then depends upon the action of some serum upon bacteria, 

 which are coped with in the body, first by the action of the serum, and then 

 by the leucocytes. This opsonic substance, like the amboceptors, sometimes 

 disappears from the blood. It is thermostabile. 



The quantitative action of phagocytosis may be estimated by Leishman's 

 method. He mixed blood and an emulsion of bacteria in salt solution in equal 

 quantities, and allowed them to stand for 30 minutes in the incubator. After 

 this the mixture was stained and the average number of bacteria per leucocyte 

 was obtained. The result was known as the phagocytic index. 



Wright has devised the following technique. Young cultures, a few hours 

 old, are employed. These are scraped off agar tubes and mixed with salt so- 

 lution. After this has sedimented, the supernatant fluid is separated from the 

 bacterial masses by a centrifuge; is pipetted off, and preserved. 



Washed leucocytes are obtained by collecting 2 c.c. of blood in 30 c.c. of salt 

 solution containing i percent citrate of soda to prevent blood coagulation. 

 The serum and citrate of soda are separated from corpuscles by washing twice 

 in a centrifuge. The upper layer of the sediment is rich in washed leucocytes, 

 and is used in the experiments. 



To obtain the opsonic index, blood serum from various cases is collected. In 

 the case of staphylococcus infection say furuncle the blood serum is drawn 

 from the patient and, with equal portions of an emulsion of staphylococci 

 (young culture), and a suspension of washed corpuscles, is thoroughly mixed 

 in a pipette, which after the ends are sealed, is placed in an incubator for 15 

 minutes. A drop of the mixture is then spread upon a slide; fixed, and stained 

 with Jenner's stain. The number of staphylococci in 50 polynuclear leucocytes 

 is determined and divided by 50 to obtain the average. 



At the same time that this experiment is being performed, some norma 1 



