436 BACTERIOLOGICAL CHEMISTRY 



with the mid-piece, although a Uttle was sometimes carried 

 along with the end-piece. The active substance in zymin 

 is an insoluble carbohydrate called zymosan. The same 

 workers in 1926 showed that the addition of small amounts 

 of ammonia to serum destroyed the complement action 

 and established that it did so by acting on a " fourth 

 component." The fourth component is heat stable, but 

 is not identical with the third component since it is not 

 adsorbed by zymin. The majority of the fourth com- 

 ponent is associated with the end-piece. It is specifically 

 removed by treatment with ammonia, methylamine, 

 ethylamine, hydrazine or phenylhydrazine, other alkalies 

 completely destroying all the factors, as does ammonia 

 if it is allowed to react for too long. All these compounds 

 can react with the potential aldehyde group of carbo- 

 hydrates and it is suggested that the fourth component 

 may be a carbohydrate carried by the pseudoglobulin 

 end-piece. The claim of Takano that the loss of activity 

 of complement on treatment with ether or chloroform or 

 viper venom was due to the lipoid nature of the fourth 

 component is inaccurate since treatment of dried com- 

 plement with lipoid solvents has no effect on the fourth 

 component, the loss of activity of liquid serum being 

 due to denaturation of the proteins. 



The symbols C^l, C'2, C'3andC^4 have been suggested 

 for midpice, endpice, third component and fourth com- 

 ponent, respectively. Since the ' serves no apparently 

 useful purpose it is proposed to omit it here. 



In hsemolytic reactions components Cl, C2 and C4 

 combine with sensitised sheep red blood corpuscles but 

 C3 does not. Although Cl combines with red cells in 

 the absence of C4 it is hsemolytically inert unless C4 

 combines previous to, or simultaneously with, it. Al- 

 though C3 is not fixed by antibody-red-cell aggregates 

 it is essential for hsemolysis and acts on the sensitised 

 cells after fixation of the otlier components^ It appears 

 to liave catalytic activity. 



