ZOOLOGY, ENTOMOLOGY, AND MEDICINE 243 



parts of the leukocytes, blood serum, and bacterial emulsion are 

 drawn up into a small capillary tube, and mixed in a watch 

 crystal and again drawn into the tube. The tube is then 

 sealed and incubated at blood temperature for about twenty 

 minutes. The mixture is again shaken and smears made and 

 stained with a good blood stain. Many of the bacteria will 

 be found to have been assimilated by the leukocytes. The con- 

 tents of a fair number, about a hundred, are counted and an 

 average made. Simultaneously with this test, a control is 

 made of a normal individual, one hundred leukocytes are 

 counted and an average taken ; the results of the latter divided 

 into the result of the person being tested, give the opsonic 

 index — i.e., if the normal one's average is four bacteria per 

 leukocyte and the tested one is three per leukocyte, we would 

 have three divided by four equals .75 ; in other words, three- 

 quarters of the quantity of opsonins only are present in the 

 serum of the tested patient. 



The opsonic index is increased by the injection of toxins 

 or bacterial bodies into healthy tissues, thereby the phagocytic 

 power of the body is increased in proportion to the increase 

 in opsonic powers. 



Vaccines or bacterial vaccines or bacterins as they are now 

 called, serums of anti-toxin, belong to the class of biologic 

 preparations. These do not replace drugs, but are new means 

 in treating diseases caused by bacterial infection, and are 

 given with but one purpose in view, that is to produce im- 

 munity whereby the patient may be able to overcome and 

 cease temporarily at least to be susceptible to attacks by path- 

 ogenic bacteria. 



Bacterines consist of suspensions of killed bacteria. In the 

 preparations of these no animals are needed. The bacteria for 

 a specific bacterine or vaccine are grown on suitable media, 

 removed from this media by washing with normal salt solu- 

 tion, killed by heat and then emulsified in salt solution. 



The bacteria are then counted in order that a specified num- 

 ber may be administered at each dose and put up in suitable 

 containers. Bacterines are used to produce active immunity 

 when injected, they stimulate the patient's body cells to pro- 

 duce its own anti-bodies, including such substances as agglu- 



