An 



consider the insolubility of Ca soaps it is possible, that the indiffiisible 

 part of the plasma Ca will consist wholly or partially of soaps. It 

 is easily to be shown, that complete precipitation of the blood Ca 

 is followed by a marked decrease of surface tension. 



Surface tension of one cc. of freshly taken human serum is 53 

 dynes/cm; when 0,3 ccm. of a saturated solution of oxalate of 

 ammonium is added, it decreases to 50, 48, 46 dynes/cm. The action 

 of NaFl is similar. 



Further if at little acid is added to the plasma, the fatty acids 

 must be liberated from the eventually existing Ca soap compound. 

 This proved to be the case; the amount of HCl necessary to lower 

 the surface tension of serum from 52 to 45 dynes is exactly 

 equivalent to the potential alkalinity of that serum. So it is probable 

 that in normal blood also a great deal of the fatty acids are circu- 

 lating in the form of Ca compounds. Direct chemical analysis will 

 have to bring further evidence. 



Till now we only examined the inactivation of oleic acid; the 

 saturated fatty acids appear to be bound in the same way, but the 

 physiologically important highly unsaturated linolenic acid give Ca 

 salts, which lower the surface tension of the balanced salt solution 

 to 38 Dynes. In accordance with this the blood or plasma it is not 

 capable to maintain its surface tension if a small amount of isotonic 

 neutral emulsion of linolenic acid is added, contrary to what occurs 

 when oleic acid is given. This is seen from the following experiment. 



Surface tension of fresh human serum 53 dynes p. cm. 



-|- 0.001 N linolenic acid emulsion 47 „ , 



+ 0.002 N , 46 „ 



+ 0.003 N „ „ , 46 „ 



+ 0.004 N 44 „ 



+ 0.005 N 43 „ 



Although linolenic acid also is in plasma subject to considerable 

 capillary inactivation, this process is not so complete, that the surface 

 tension can be maintained absolutely constant. This fact must be 

 explained by the capillary activity and solubility of the linolenate 

 of Ca. 



By these circumstances the higher unsaturated fatty acids circula- 

 ting in the blood must have a great biological importance, because 

 their Ca inactivation is failing. Therefore these acids must be bound 

 by plasma colloids or corpuscles with decrease of interfacial tension. 

 If now the inactivation of fatty acids extracted from corpuscles is 

 compared in serum and in salt solution with the process described, 

 it appears that these substances have the same properties as saturated 



31 



Proceedings Royal Acad. Amsterdam. Vol. XXVI. 



