182 THE PRINCIPLES OF IMMUNOLOGY 



laked the antigenic cells in doses of 0.0015 c.c. and fixed complement in 

 the presence of o.ooi c.c. ox serum. The immune serum prepared 

 against ox serum hemolyzed ox cells in doses of 0.05 c.c. but fixed 

 complement when combined with only 0.000,001 c.c. of ox serum. The 

 immune serum against ox serum had only about one-thirtieth the 

 hemolytic power of the immune serum prepared against ox cells but was 

 looo times more powerful in fixing complement. They found that 

 ox cells can absorb hemolysin from an immune serum without removing 

 the precipitating or complement-fixing activity and conclude, in oppo- 

 sition to the hypothesis offered at the end of the preceding paragraph, 

 that the complement-fixing body and the hemolysin are distinct and 

 separate immune bodies. 



Fixation of the Complement of Natural Hemolysins. In the case 

 of natural hemolysins the complement in many instances is apparently 

 in a state of close combination with the -thermostable lytic body. The 

 entrance of such complements into the phenomenon of complement 

 fixation has only rarely been demonstrated and then only in the case 

 of those naturally hemolytic sera in which it is possible to absorb 

 hemolytic amboceptor at o C. without at the same time removing 

 the complement. 



Nature of Antigen and Amboceptor. The chemical character of 

 the antigen and amboceptor have been studied more particularly in 

 connection with investigations of the Wassermann test and will be 

 considered in the discussion of that application of complement fixation. 

 It may be said at this place, however, that the complement-fixing 

 immune body will resist the ordinary inactivating temperature of 56 C. 

 and is therefore to be regarded as thermostable but is destroyed by 

 75 C. for one hour. The antigen is thermostable in the same sense 

 but is reduced in activity at 75 C. but not destroyed until 100 C. 

 is reached. 



Inhibition of Complement other than by Fixation. Of great im- 

 portance are the factors that exercise an influence upon complementary 

 activity. Those which operate on the living animal have been discussed 

 in the chapter on Cytolysins (see page 127). There was also presented 

 a brief discussion of physical conditions such as heat, exposure to light, 

 desiccation, etc. All these factors must be considered in interpretations 

 of complement fixation, and in addition it is considered desirable to 

 present certain other conditions which may be gathered into three classes 

 (a) chemicals, (&) various tissues and fluids, (c) antisera. 



Anti-complementary Chemical Agencies. The salt concentration 

 of the media for complement fixation is extremely important and reaches 

 its optimum at a point isotonic with the body fluids. The action of 

 complement is decreased in hypotonic and absent in salt free media. 

 Examination of this phenomenon leads to the conclusion that such 

 action is upon complement rather than upon amboceptor, and Ferrata is 

 of the opinion that the important change is the splitting of the comple- 

 ment into mid-piece and end-piece. Under these circumstances the 

 mid-piece may be bound to the amboceptor-antigen complex, but as 



