473 



surface activit}' is a property to wliicli combining power and liae- 

 moljtic action are inliinaleiy related, and secondly because llie 

 surface tension of small a amounla of blood can be measured accu- 

 rately and easily by the torsion balance method '). 



The surface-tension of a neutral highly diluted solution of fatly 

 acids is n)ucli lower than the static surface tension of i)loo(l lU' 

 serum. This fact already indicates that the fatty acids of blood 

 cannot occur in the free stale but must be bound somewhere. The 

 minutest trace of free fatty acid must reveal itself immediately by 

 a marked decrease of static surface tension, but the capillary- 

 activity of the protein-fatty acid compounds also is, as far as we 

 know, so intensive, the a decrease of surface tension plasma-air 

 should be observed if an added fatty acid was bound as protein- 

 compound. 



The possible combination of protein and fatty acids may supposed 

 to be primarely chemical or adsorptive; the last form would be 

 probable by the intensive surface activity of these substances. 



In the following table it is shown how the surface tension serum- 

 air changes when small quantities of a diluted neutral emulsiou of 

 fatty acids are added. 



Surface tension of fresh human serum 52 Dynec.M. 



-j- 0.001 N oleic acid in neutral emulsion 52 „ 



-h 0.002 N „ . „ „ 52 „ 



+ 0.003 N 52 „ 



+ 0.004 N „ „ „ „ 51 



+ 0.005 N 47 



+ 0.006 N „ „ „ „ 45 „ 



+ 0.007 N „ 42 „ 



+ 0.008 N „ „ „ „ 41 



+ 0.009 N „ „ . 39 



+ 0.010 N „ „ „ „ 39 „ 



It is seen, that 0,004 N. oleic acid may be added to seiiim 

 without change of surface tension; when more acid is given, a 

 gradual decrease of surface tension takes place till the value of 

 ± 40 dynes/cm. has been reached. A further lowering is only 

 to be seen, if large amounts of fatty acid are added. We will not 

 delay upon the explanation of the gradual decrease of tension, but 

 try to investigate the mechanism by which the plasma can preserve 

 its original tension. Any marked lowering of this tension must be 

 considered abnornnil. 



The constancy of surface tension indicates that the researclied 



') Brinkman and Van Dam. Munch, raed Woch. 1550 (1921). 



