VACCINE-THERAPY 61 



scope, and note taken of the disposition of the bacteria up 

 to an hour, but usually half an hour is long enough. If 

 the reaction is a positive one, the bacteria, if motile, will 

 lose their motility, and collect themselves into clumps — 

 agglutinate. On the contrary, if the reaction is a negative 

 one no clumping will take place. 



Another method of making use of the agglutinative 

 reaction for diagnostic purposes is to add a measured 

 volume of serum to a known quantity of the culture media 

 in a test-tube. In due course, if the reaction is a positive 

 one, a white precipitate will form and settle on the bottom 

 of the tube. This is known as the " precipitation test," and 

 has the advantage of being very simple in its application. 



Bacteriolysins. 



Under this heading, we find there exists in the blood 

 protective bodies capable of destroying bacteria by solu- 

 tion — bacteriolysins — and the process is known as " bac- 

 teriolysis." It appears that the serum of the blood soon 

 loses its bacteriolytic properties when separated from the 

 tissues. 



Experiments have proved that the solution of the 

 microbes is brought about by the interaction of at least 

 two substances, one of which is present in all serums in 

 the living body, but disappears on heating and on keeping 

 at room temperature in from five to eight days. The 

 other is more stable, and is produced during the process 

 of inoculation. The former unstable body, found in all 

 animals, is termed "complement"; the latter, produced 

 in the processes of immunity, is called the " amboceptor." 



It is presumed the amboceptor links the complement to 

 the bacterium, but the complement remains free if the 

 suitable amboceptor is not present, and bacteriolysis does 

 not take place (Ehrlich) (Fig. 30). 



It is upon this process of bacteriolysis that Pfeiffer's 

 reaction depends, which is useful in recognizing the exact 

 species of bacteria. 



