DOUGLAS M. SURGENOR 



cytosis promoting factors, they are effective at extremely low 

 concentrations. Under the conditions presently being used for 

 their assay it has not been possible to differentiate their effect 

 on the white cells. In solubility, electrophoretic mobility, and 

 other properties, however, they differ markedly. Neither pos- 

 sesses hemolytic complement or C 3 activity, but it remains to be 

 established whether they represent other components of comple- 

 ment. Treatment of serum by the procedure described by 

 Pillemer (29) for removal of properdin resulted in slightly de- 

 creased phagocytosis promoting activity, suggesting that pro- 

 perdin may be involved but not as a primary factor. 



It may be anticipated that detailed study of the mechanisms 

 by which these purified protein components interact with the 

 white cell, whether by affecting the physical properties of the 

 cell membrane, by enzymatic triggering of a metabolic re- 

 sponse, or in some other fashion, will clarify many conflicting 

 views on the nature and action of the opsonins of serum. As 

 with so many other systems, the value of prior purification of 

 components as a prerequisite to determination of physiological 

 roles is well illustrated by properdin and the phagocytosis 

 promoting factors. 



Clotting Mechanisms 



The complex series of interactions concerned with blood 

 coagulation represents one of the most active areas of investiga- 

 tion today. Although certain isolated reactions, i.e., the con- 

 version of fibrinogen to fibrin by thrombin, appear to be well 

 characterized, it is not yet possible to draw a picture that would 

 not arouse intense debate by protagonists on various sides. The 

 problem is an intriguing one. Less than 20 years ago the most 

 widely accepted mechanisms involved a relatively small number 

 of reactants; in a recent review, Alexander (2) has proposed a 

 "Modern Scheme of Coagulation" which includes over 20 inter- 

 acting components. Clearly, nature has evolved an elaborate 

 and delicately balanced system of enzymes, enzyme precursors, 



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