470 STUDIES IN GENERAL PHYSIOLOGY 
in weight occurs more slowly than the increase in the con- 
centration of the external solution. 
Both results point to the fact that an increase works in 
the same sense as a decrease in the amount of water con- 
tained in the cells, for both lead, apparently, to an increase in 
the osmotic pressure within the cells. 
It is generally stated that muscles always twitch in con- 
centrated salt solutions in consequence of the loss of water 
which they suffer, and Miss Cooke was inclined to see in 
these twitchings the cause of the increase in the osmotic 
pressure in the muscles immersed in hyperisotonic salt solu- 
tions. I noticed, however, that these twitchings always 
occurred in 1.05 and 1.4 per cent. solutions; that they occur- 
red only rarely in 1.7 per cent. solutions, and that they 
never occurred in 2-2.8 per cent. solutions. It is possible 
that they occurred in the latter case only during the first few 
moments after immersion and then ceased. They might in 
this way have escaped my notice. One cannot,’ therefore, 
simply say any longer that the withdrawal of water brings 
about contractions in the muscle, but one must add that this 
occurs only when the difference in osmotic pressure between 
the outer solution and the muscle is not too great, or, perhaps 
more accurately, when the concentration of the surrounding 
solution is not too high. 
The fact that the loss of water by the muscle increases 
more slowly than the difference in the osmotic pressures 
between the outer solution and the muscle is supplemented 
by the behavior of the muscle when left for a long time in 
0.7 per cent. and hyperisotonic sodium-chloride solutions. 
The decrease in weight soon comes to a standstill, and the 
muscle begins to take up water so that in eighteen hours its 
weight is greater than its original weight. This occurs even 
when the muscle is kept in a 2.8 per cent. NaCl solution! 
This fact that the ‘‘injured” muscle is able to take up 
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