S.. C. BROOKS 199 



In this scheme R represents choline glycerophosphoric acid or some 

 similar substance, and, since compounds of lower fatty acids are 

 markedly lacking in hemolytic power, the two fatty acids may each 

 be supposed to contain at least ten carbon atoms. One of the acids 

 is for two reasons supposed to be unsaturated: because compounds 

 of unsaturated fatty acids are in general more hemolytic than those 

 of the corresponding saturated acids, as shown by Lamar i^^ and 

 because this furnishes a molecular grouping known to be attacked 

 by light^° with a consequent break in the fatty acid chain which 

 might be expected to bring about a great decrease in hemolytic 

 power.^i 



Many phenomena displayed by complement are undoubtedly 

 dependent in some way upon the physical or chemical state of the 

 serum colloids, as is shown for example in the previously noted inac- 

 tivation by acid. Sachs and Stilling^^ have shown that inulin sus- 

 pended in cold water affects complement, while if first dissolved by 

 warming the water it no longer has any effect. It is not surprising 

 then that complement is inactivated by shaking, since shaking, or 

 rather the attendant foaming, causes irreversible coagulation of pro- 

 teins, ^^ nor that processes which precipitate serum globulins should, 

 if the process is reversible, produce the so called "fractions" which 

 upon being recombined regain their hemolytic power. The conflict- 

 ing nature of the evidence about these so called fractions, as w6ll as 

 the writer's own experience with several methods of obtaining the 

 fractions, leads him to doubt the uniformity of the preparations 

 secured by different investigators. Evidently the lytic substance is 

 usually held inactive in one of the fractions, since exposure of sensi- 

 tized red blood cells to the globulin or "mid-piece" fraction results 

 in a change which makes them susceptible of lysis by the albumin 

 fraction, which is therefore supposed to combine with some element 

 in the red blood cells indirectly through the "mid-piece." It is for 

 this reason that the albumin fraction has received the name "end- 

 piece." 



29 Lamar. R. V., /. Exp. Med., 1911, xiii, 380. 



^° Ciamician, G., and Silber, P., Ber. chem. Ges., 1914, xlvii, 640. 



^^ Sfiimazono, J., Arch. exp. Path. u. Pharmakol., 1911, Ixv, 361. 



^~ Sachs. H., and Stilling. E., Z. Immunitdtsjorsch., Orig., 1917, xxvi, 530. 



3^ Ramsden, W., Arch. Physiol., 1894, 517. 



