712 MICROBIOLOGY OP DISEASES OF MAN AND DOMESTIC ANIMALS 



agglutinins and precipitins, although they bear some points of re- 

 semblance to antitoxins and complements. They possess two so- 

 called chemical groups, a "combining group" by which they enter into 

 chemical union with the bacteria and a "functional group" which 

 really sensitizes the microorganism and makes it phagocytable. 



It has been shown that the opsonins may be increased in the 

 serum of the animal or injected individual by the injection of heated 

 (60°) cultures of the specific etiological microorganisms. Such sub- 

 stances are called opsonogens or vaccines (bacterins). Vaccines are 

 used to a certain extent in the treatment of the various pus infections 

 due to the staphylococci and also in tuberculosis and pneumonia. It 

 is supposed that the opsonins are produced in the subcutaneous tissues 

 and in the muscles. 



The Opsofdc Index. — ^The concentration of the opsonins may be 

 recorded in an individual in the following ways. Suppose the leu- 

 cocytes of the infected individual take up a certain number of bacteria, 

 say an average of 5, after counting 50 to 100 polymorphonuclear leu- 

 cocytes. In this case the phagocytic index is said to be 5. Again, 

 suppose the leucocytes of the normal individual take up 15 of the bacr 

 teria in question, the average after counting 50 to 100 leucocytes 

 being always taken. The phagocytic ind^ in this case would be 15. 

 In order to determine the opsonic index of an infected individual the 

 phagocytic index of the normal individual is taken as a denominator 

 of a fraction and the phagocytic index of the infected individual as the 

 numerator of the fraction. In the above illustration this would be 

 ■ M^5) K or reduced to decimals 0.33+. The opsonic iiidex, it can bt 

 seen, is somewhat of an indication of the resistance of the particular 

 individual to the infecting microorganism in question. By the use 

 of vaccines the opsonic index may be raised to at least i.o or even 

 more, showing that the leucocytes are actively phagocytic and the 

 opsonins increased in concentration in the blood serum. In such a 

 case recovery would be indicated. When vaccines are injected in the 

 treatment of infections the opsonic index has been shown to vary from 

 time to time. Within a few hours after the injection the opsonic 

 index falls below what it was at the time of the injection. This lower- 

 ing of the index is known as the "negative phase." Following the 

 fall in the index there is a continuous rise to a point equal to what it 

 was in the beginning and above this point. This rise in the opsonic 



