Kalph W. Webster 



13 



solution. The ultimate result will be due, therefore, to a combination of osmotic 

 pressure effects with those of diffusion. 



c. Absorption from Urea Solutions.— The following table shows the absorption 

 under influence of various concentrations of urea: 



TABLE IV 



It will be seen above that a muscle, immersed in a solution of urea isosmotic with 

 ^m NaCl, gains in one hour 11 per cent., while in twenty-four hours the gain is 72 

 per cent. What do these facts denote ? If the sarcolemma be impermeable to urea, 

 as it was to cane-sugar, then, of course, we should have the phenomena controlled by 

 laws of osmotic pressure. If it be permeable to urea, as well as to water, we should 

 have, according to laws of diffusion, urea passing from point of higher to that of 

 lower concentration, or, in other words, into the muscle. An effort would be made to 

 adjust the equilibrium on both sides of this permeable membrane. Along with this 

 partial adjustment of urea, must go the adjustment of the concentration of various 

 ions on each side of the sarcolemma. A current of diffusion is thus set up, which 

 passes in both directions through the sarcolemma. The result of all this would, there- 

 fore, be an increase in weight on the part of the muscle. 



It is clear that osmotic or ionic effects cannot explain the large increase in weight 

 under influence of urea solution. The progress of absorption from urea is, markedly, 

 similar to that noted when water is used, although the absolute absorption in the latter 

 case is more marked at each interval except the final one. As the results seem to show, 

 urea easily penetrates the sarcolemma. Osmotic pressure effects cannot, therefore, be 

 considered of the first importance. Just why such a marked increase in absorption 

 occurs during the later intervals does not seem clear to the writer at present. It may 

 be that certain decided changes, such as the breaking down of urea into NH4 com- 

 pounds or the formation of amido compounds, may result in an increased osmotic 

 pressure and a resulting increase in absorption. The action of these nonelectrolytes upon 

 phenomena of absorption is markedly different from that observed in other phenomena. 

 Loeb, Lingle, Moore, Kahlenberg, True, and others have observed that, in general, 

 nonelectrolytes have little or no effect on the phenomena under observation. In these 

 experiments it is quite evident that the effect of the non-electrolytes is very marked. 



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