778 



THERMOLABILITY OF COMPLEMENT 



curve given by the unsplit and imheated control or from that given 

 by varying amounts of one fraction and constant amounts of the 

 other fraction, in each tube of the control titration. It is evident 

 that there is a broad optimal zone for the preservation of the end- 

 piece function, with a reaction of about pH 6.9 as its central and 

 highest point. At this reaction the end-piece is relatively thenno- 

 stable as compared with whole complem.ent. 



80 



70 



60 



^50 



^ 40 



^^30 



20 



10 







pH 7.4 7.2 7.0 6.8 6.6 6.4 6.2 6.0 5.8 5.6 54 52 5.0 



Fig. 5. The complementary activity in the presence of unheated mid-piece 

 of the end-piece fraction heated separately in distilled water dilution at different 

 reactions. 



A similar relative independence of the H ion concentration as com- 

 pared with whole complement is shown by the isolated mid-piece frac- 

 tion, heated in distilled water. Two experiments at 50°C. are shown 

 in Fig. 6. There is an optimal zone about pH 6.2 with a gradual fall 

 on the alkaline side and a more rapid fall on the acid side of this point. 



In the experiments with the isolated fractions the mid-piece 

 whether heated or unheated was added first to the sensitized cells 

 in order to avoid the peculiar modification described by Brand." 

 The curves represent therefore the degree of complete or irreversible 

 inactivation of the fractions. 



