1913] OSTERHOUT—PROTOPLASMIC CONTRACTIONS 451 
The effect of unbalanced solutions on permeability has been dis- 
cussed elsewhere.* 
The facts described above have an important bearing on certain 
theories recently advocated by some biologists and colloid chemists. 
According to these authors, the effects which are usually attributed 
to osmotic pressure are in reality due to imbibition or to the giving 
up of water by the protoplasm, without the intervention of a semi- 
permeable membrane. It would not be possible on this theory to 
account for the shrinkage of the protoplasm of a cell to half its 
volume when transferred from sea water to distilled water, espe- 
cially when the process is irreversible. But the explanation given 
above—the increase of permeability of a semipermeable membrane 
—not only agrees with the facts described here, but also with those 
derived from a variety of other material, and by the use of entirely 
different methods. 
LABORATORY OF PLANT PHYSIOLOGY 
VARD UNIVERSITY 
4 Science, N.S. 35:112. 1912; 362350. 1912. 
