782 THERMOLABILITY OF COMPLEMENT 



at these reactions^" which is caused by the high concentration of 

 the common Na ion. On the acid side of pH 6.1 to 6.4 the protein 

 exists in amounts increasing with the acidity in the cationic condition. 

 We should expect a similar depression in the ionization of the protein 

 in this form to be caused by the excess of the common CI ion, but 

 since at these reactions the destruction of complement is as great 

 in the presence as in the absence of salt it is apparent that the be- 

 havior of the protein as cation is different from that as anion. This 

 conclusion was suggested by Brooks'^ from a somewhat different 

 evaluation of similar data. 



CONCLUSIONS. 



1. The destruction which complement undergoes on being heated 

 in dilution in distilled water is least at a reaction between pH 6.1 

 and 6.4. This depends upon the relative preservation of the mid- 

 piece function at this point. This reaction represents probably the 

 isoelectric point of a compound of the euglobuHn with some substance 

 present also in serum. 



2. During the process of thermoinactivation it is chiefly or entirely 

 the ions of this euglobulin compound which react, and these combine 

 or interact with substances contained in the pseudoglobulin and 

 albumin fraction. 



3. The behavior of the euglobulin is different in the anionic and 

 in the cationic condition, since on the acid side of pH 6.1 to 6.4 the 

 destruction by heat increases as rapidly with the acidity in the pres- 

 ence as in the absence of NaCl. On the alkaline side of this point 

 the presence of NaCl protects complement from destruction because 

 of the depression in the ionization of the euglobulin. 



20Loeb, J., J. Gen. Physiol, 1918-19, i, 39, 237, 363, 483, 559. 



