THE EFFECTS OF ELECTROLYTES ON GELATIN AND 
THEIR BIOLOGICAL SIGNIFICANCE. 
I. THE EFFECTS OF ACIDS AND SALTS ON THE PRECIPITA- 
TION OF GELATIN BY ALCOHOL. 
byw. O. FENN, 
(From the Laboratory of Plant Physiology, Harvard University, Cambridge.) 
(Received for publication, December 21, 1917.) 
The biologist can hardly hope to find a complete explanation 
of the complicated effects of electrolytes upon protoplasm until 
the chemist can give him an explanation of their almost equally 
complicated effects upon the purified constituents of protoplasm. 
In order to obtain more complete information concerning the 
effects of electrolytes upon proteins, the precipitation of gelatin 
by alcohol has been studied. This property of gelatin is more 
simple to measure and more sensitive to small variations in the 
salt content of the solution than its viscosity, swelling, or tem- 
perature of gelation. This method has yielded, therefore, more 
complete data than have hitherto been obtained. Pending a 
more detailed inquiry into the reactions involved, it is deemed 
advisable to publish the facts obtained, omitting the theoretical 
interpretation. 
Description of the Method. 
The method which was worked out for the investigation has 
already been briefly described! together with some of the re- 
sults which are of particular interest to the biologists. It con- 
sists essentially in adding 95 per cent alcohol to 5 cc. of the 
gelatin-electrolyte mixture until an opaque precipitate is pro- 
duced. The sharpness of the end-point varies characteristically 
with the particular electrolyte and the particular concentration 
used but can ordinarily be determined to within 0.1 cc., which is 
1 Fenn, W. O., Proc. Nat. Acad. Sc., 1916, li, 534, 539. 
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