March 21, 1913] 



SCIENCE 



433 



These two series of results may be con- 

 sidered as identical within the limits of 

 error. They prove that proteins in solu- 

 tion attract water from the muscle solely 

 according to their osmotic pressure and 

 not according to any other real or assumed 

 quality. They prove also that the salts 

 and not the proteins of the blood deter- 

 mine the exchange of water with the 

 tissues. 



R. Lillie has shown that the addition of 

 acid increases the osmotic pressure of a 

 protein solution, but the increase is too 

 small, even in dialyzed serum, to influence 

 the velocity of water absorption, as the 

 following figures show. 



CHANGE IN WEIGHT OF TWO MUSCLES 



I think all these experiments prove con- 

 clusively, (1) that colloidal solutions influ- 

 ence the absorption of water in the tissues 

 solely by their osmotic pressure; and (2) 

 that this osmotic pressure is so small in 

 comparison with that of the salts in the 

 liquids of the body that their influence is 

 in general practically negligible.^* 



IV. PKRMEABLE AND NON-PEEMEABLE 

 SOLUTES 



The existence of semi-permeable walls 

 which allow the water but not the solute 



" The erroneous idea that the attraction of 

 water by blood serum is determined by proteins 

 may have originated through the arbitrary as- 

 sumption that the phenomenon of imbibition 

 found in solid colloids is retained by the colloids 

 in solution. This reasoning is, however, not war- 

 ranted, since it is possible that in solid colloids 

 conditions for the absorption of water may exist 

 which cease to exist when the colloid is dissolved. 



to diffuse is the prerequisite for the mani- 

 festation of osmotic pressure. It is well 

 known that Overton showed that dissolved 

 substances which diffuse easily into the cell 

 do not produce any osmotic effect. The 

 permeability of cell walls for alkaloids can 

 be directly demonstrated by their reaction 

 with the tannic acid of the cells, and Over- 

 ton showed that when added to an isotonic 

 salt solution the alkaloids will not alter the 

 water equilibrium. The substances which 

 thus diffuse readily into the cells are alco- 

 hols, aldehydes and many other compounds 

 which often show a relatively high degree 

 of solubility in lipoids. The difference in 

 the behavior of substances which are sol- 

 uble in the cell wall (like alcohol) and non- 

 soluble (like sugar) is illustrated by the 

 following experiments by Overton. ^° 



In 0.2 per cent. NaCl -f- 2.66 per cent, 

 mannit (together equi-molecular with .7 

 per cent. NaCl) the gastrocnemius of a 

 frog kept its weight for nine hours un- 

 altered. In 0.2 per cent. NaCl + 2 per 

 cent, methyl alcohol (approximately equi- 

 molecular with a 1.6 per cent. NaCl solu- 

 tion), the muscle absorbed water as power- 

 fully as in a pure 0.2 solution of NaCl. 

 Only those substances which can not dif- 

 fuse into the cell can assist in the exchange 

 of water between tissues and the liquids of 

 the body; exactly as Avogadro's law de- 

 mands. 



It is generally assumed that there is only 

 one type of semi-permeable membranes, 

 namely, those permeable for water, but not 

 for neutral salts or sugars. This type is 

 the most common. But there are at least 

 two other types of semi-permeability. 

 Some membranes are permeable for water 

 as well as salts and sugars, but not for 

 colloids. The fertilization membrane of 

 the sea urchin egg {Strongylocentrotus 



"Overton, Pfliiger's Archiv, Vol. 92, p. 115, 

 1902. 



