S. C. BROOKS 187 



accompanied by changes which are at least quahtatively like those 

 displayed by the pure proteins themselves under radiation. Since 

 the lytic principle can be nearly destroyed without any perceptible 

 alteration of the serum proteins, we are forced to the conclusion that 

 complement is not one of the serum proteins, and is, to a certain 

 extent at least, independent of them. 



II. 



This must not be thought to mean that the hemolytic power of 

 serum is wholly independent of proteins under all conditions. The 

 experiments of Jacoby and Schiitze'^ on the inactivation of comple- 

 ment by shaking, those of Michaelis and Skwirsky^ on the effect of 

 proteases on complement, and many others indicate the contrary. 



To obviate confusion it may be well to point out that while the 

 hemolytic substance is probably not a protein, as explained in the 

 preceding section, this is not incompatible with the fact that comple- 

 ment may be profoundly affected by changes in the serum proteins; 

 inactivation may be the direct effect of some agent, e.g. light, or it 

 may be indirect and due to the effect of a change produced by the 

 action upon serum proteins of such an agent as a protease. The 

 serum proteins thus altered may then act upon the lytic substance. 



The following experiments bear out this idea, since they suggest 

 that acid may inactivate complement not by means of its effect upon 

 the lytic substance itself, but by altering the state of the serum pro- 

 teins. 



It has long been known that complement could be made inactive 

 by the addition of acid and alkali, and that if more than a small 

 amount of acid or alkali was added the inactivation was not reversi- 

 ble by subsequent neutralization of the added reagent. The precise 

 limits of pH value between which inactivation is still reversible have 

 not heretofore been determined. 



Fresh guinea pig serum was diluted to 20 volumes with 0.85 per 

 cent NaCl solution^ and kept in containers immersed in ice water 



^Jacoby, M., and Schutze, A., Berl. klin. Woch., 1909, xlvi, 2139. 



^ Michaelis, L., and Skwirsky, P., Z. Immunitdtsforsch., Orig., 1910, vii, 497. 



^ The balanced solution employed for dilution throughout all other parts of 

 this work would have resisted changes in reaction by reason of its bicarbonate 

 content, and hence could not be used in this particular operation. 



