190 



MECHANISM OF COMPLEMENT ACTION 



only within 0.2 pH units, because they were judged only on the basis 

 of the approximate colors, in samples of the acidulated complement, 

 of two or more of the following indicators; phenol red, brom cresol 

 purple, methyl red, and brom phenol blue. No standard comparison 

 solutions were used. Bearing these facts in mind it will be seen that 

 the experiments agree in showing very little change in the efficiency 

 of complement (perhaps even a slight increase in some cases) as long 

 as the hydrogen ion concentration is less than pH = 6.0; when the 



TABLE II. 



The Permanent Effect of Temporary Acidulation on Radiated and Unradiated 



Complement. 



pH = 5.5, there is some decrease in the hemolytic power, and as it 

 exceeds 5.0 there is a rapid drop in efficiency, complete inactivation 

 being the result at pH = 4.3. The data for these experiments are 

 given in detail in Table II. 



There is a remarkable parallelism between this behavior and the 

 known characteristics of the serum proteins. The serum proteins 

 are usually classified as eu- and pseudoglobulins and albumins accord- 

 ing to their solubility in water and in salt solutions; but there are no 

 sharp divisions between these groups. The isoelectric point of euglo- 

 bulins as prepared by Rona and Michaelis^^ is given by them as 3.6. 



^^ Rona, P., and Michaelis, L., Biochem. Z., 1910, xxviii, 193. 



