192 MECHANISM OF COMPLEMENT ACTION 



If this is true then the lytic substance may be inactivated in either 

 of two ways: either directly, as by ultra-violet light; or indirectly by 

 means of agents affecting other serum constituents; e.g., the proteins^* 

 (Table III). 



These same experiments show also that radiation sufficient to destroy 

 the hemolytic power of serum may fail to have any appreciable effect 

 on the serum proteins; otherwise there should be a difference between 

 radiated and normal complement in their susceptibility to inactiva- 

 tion by acids (Fig. 1 and Table II). Differences between radiated 

 and normal complement do occur occasionally, but they are so irregu- 

 lar as to have no obvious general significance. Radiation fails to 

 sensitize complement to either heating (Section I) or acidulation, and 

 the two sets of experiments substantiate each other in this respect. 



III. 



In view of the fact that surface tension of complement has been 

 thought by some^^' ^^ to be connected directly with its hemolytic 

 power it is interesting to note the change in surface tension taking 

 place when complement is inactivated by ultra-violet light. 



The surface tension of 5 per cent complement solution was meas- 

 ured by means of a Traube stalagmometer and was found to decrease 

 slightly (Table IV and Fig. 2) , Measurements of the time of outflow 

 made at the same time are probably not reliable because of the pres- 

 ence of occasional wisps of cotton in the solutions, but since they 

 seem to indicate a change in viscosity they are also given: if there is 

 any definite change of viscosity it is a decrease. 



^^ In this connection it should be pointed out that changes in hydrogen ion con- 

 centration play no part in the ordinary course of photoinactivation. Samples of 

 5 per cent complement were taken immediately after radiation for various lengths 

 of exposure and their hydrogen ion concentration determined by the addition of 

 an appropriate amount of phenol red and comparison of the resulting color with 

 that produced in solutions of known hydrogen ion concentration. The least 

 active sample had been reduced to a relative efficiency of 23.6 per cent. There 

 was an irregular variation of between pH = 7.55 and 7.50, which is so small as 

 to be utterly negligible (Table III). The complement is at all times exposed 

 to a hydrogen ion concentration the same as that prevailing in the blood plasma. 



15 Traube, J., Biochem. Z., 1908, x, 371. 



16 Traube, T, Biochem. Z., 1908, x, 380. 



