IMMUNITY EXPERIMENTS. I2Q 



sterile slide; deposit a small drop fora hanging-drop preparation and 

 draw up the remaining mixture into the same tube and again incubate. 

 The time and dilution with which the culture becomes nonmotile and 

 granular (bacteriolytic disintegration) should be recorded. Controls 

 with normal serum are always necessary. 



DEVIATION OF THE COMPLEMENT. 



It has been found that if there is not sufficient immune body in a 

 mixture of normal serum, containing abundant complement, and 

 bacterial emulsion, only a portion of the bacteria present will be 

 destroyed. Increasing the amount of immune body with a constant 

 quantity of normal serum, we reach a point where all the bacteria are 

 destroyed. Now, if we continue to increase beyond this point the 

 addition of immune serum, the destruction of the bacteria ceases, and 

 the cultures will again contain myriads of living bacteria. 



To carry out the test, make a series of tubes containing mixtures of 

 bacteria with the same quantity in each of normal serum. Thus, each 

 tube contains 1/2 c.c. of bacterial emulsion and 1/2 c.c. of i-io normal 

 serum. Now inactivate a tube of i-ioo immune serum and to each of 

 the tubes of normal serum and bacterial emulsion add increasing 

 drops of the inactivated i-ioo immune serum. Thus, i drop to No. i 

 tube; 2 drops to No. 2 tube and so on. After incubating for 2 hours, we 

 take a pipette and plate out a fraction of a drop in an agar plate. The 

 limit at which bacteriolysis is complete is show r n by there being an 

 absence of colonies. 



Beyond or below that point colonies are more or less abundant. 

 The explanation of this phenomenon of deviation or deflection of the 

 complement is that where we have an excess of amboceptors for 

 available receptors on the bacterial cells, only a portion of the ambo- 

 ceptors can attach themselves to their specific bacteria. The free 

 amboceptors, not being able to form a union with the bacterial cell 

 receptors (for which they have a greater affinity), combine with the 

 complement present. Unless the complement be in excess, there will 

 be no free complement left to join onto the amboceptors attached to the 

 bacterial cells, and consequently bacteriolysis does not take place and 

 the plate cultures show an abundance of colonies. 

 9 



