452 MICROBIOLOGY 



leucocytes. Neufeld and Rimpau 21 discovered a third element 

 in blood serum which they claimed sensitized the bacteria but 

 did not act on the leucocytes. They proposed the name bac- 

 teriotropic for these sensitizing substances. 



Opsonin is a substance elaborated by the tissues and which 

 sensitizes bacteria for leucocytes thereby increasing phago- 

 cytosis. This substance exists, to a certain extent, in normal 

 serum, and can be increased by active immunization with dead 

 bacteria or bacterial products. The question at present is to 

 determine whether the normal opsonins and those found in 

 immune animals are identical. As phagocytosis is one of the 

 essential agencies in the production of immunity, and as this 

 process is intensified by the introduction of the bacteria 

 causing the infection, autogenic vaccines for various infections 

 were introduced. A special technique for determining the in- 

 creased phagocytosis in the blood of the infected individual has 

 been introduced.* Hektoen 22 found in a careful study of 



21 Neufeld and Rimpau. Deut. med. Wochenschrift, Bd. XL 

 (1904) p. 1458. 



^Hektoen. Jour, of Inf. Dis., Vol. V (1908) p. 249. 



* This method as described by Hiss and Zinnser taken from 

 Wright is as follows: "The three factors necessary for the perform- 

 ance of an opsonic test are (1) the blood serum to be tested; (2) 

 an even emulsion of bacteria and (3) leucocytes. 



'"1) Blood serum is obtained by bleeding from the finger and 

 receiving the blood into glass capsules. These are sealed at both 

 ends; the blood is allowed to clot; and the separation of serum is 

 hastened by a few revolutions of a centrifuge. 



"(2) The bacterial emulsion is obtained by rubbing up a few 

 loopfuls of a twenty-four-hour slant agar culture with a little 

 physiological salt solution (0.85 per cent) in a watch-glass. A very 

 small amount of salt solution is used at first and more is gradually 

 added, drop by drop, as the emulsion becomes more even. The final 

 breaking up of the smaller clumps is best accomplished by cutting 

 off very squarely the end of a capillary pipette, placing it perpen- 

 dicularly against the bottom of the watch glass, and sucking the 

 emulsion in and out through the narrow chink thus formed. 



"Emulsions of tubercle bacteria are more difficult to make. The 

 bacteria filtered off in the manufacture of old tuberculin are com- 

 monly used. These are washed in salt solution on the filter, and are 



