QO IMMUNITY 



quantities, and allowed them to stand for thirty 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 

 solution. 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 coagula- 

 tion. 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 staphylo- 

 cocci (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 fifteen 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 poly- 

 nuclear leucocytes is determined and divided by 50 to obtain the average. 



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

 serum should be used in another experiment; an emulsion of staphylococci 

 and washed leucocytes being used as above. After pursuing the same steps 

 in this experiment as in the first, the average number of staphylococci per 

 leucocyte is determined. 



Tq obtain the opsonic index, it is necessary to know the ratio of staphylo- 

 cocci in the leucocytes treated with furuncular serum and with normal serum. 

 If the normal serum leucocytes contained 10 staphylococci, and the furun- 

 cular serum contained 15, the index would be 1.5. 



In the case of tubercle bacilli, the latter must be heated to iooC. to kill 

 them, otherwise they will be agglutinated by the serum, and a homogeneous 

 emulsion will not be obtained. After heating, the clumps must be broken up 

 by grinding the masses in an agate mortar, adding a little salt solution from 

 time to time until the mass is thoroughly broken up. The bacilli must then, 

 after phagocytosis, be stained by carbol fuchsin and decolorized with acid 

 alcohol. If the leucocytes are left too long in contact with the organisms 

 they may become so engorged as to prevent counting, the number increasing 

 from 5.7 percent after five minutes to 28.5 percent in two hours. 



Highly immunized anti-bacterial serums have much greater opsonic powers 

 than have normal ones, anti-streptococcus and anti-pneumococcus sera 

 being especially pwerful toward streptococci and pneumococci. It is pos- 



