314 NEWTON BALDWIN GREEN 



enough to overbalance the OH ions until the concentration is 

 considerable. As this point is approached the precipitability is 

 of course increased and in the case of protoplasm the penneability 

 is decreased. After the isoelectric point is attained the pre- 

 ponderance of cations causes the gelatine to behave as though 

 only one salt were present, that is the precipitability decreases. 

 Fenn showed that this process actually did occur in gelatine 

 and he demonstrated a remarkable likeness between his curves 

 o^" precipitability and Osterhout's^ curves plotted from the 

 changes in the electrical resistance offered by discs of Laminaria 

 frond. To complete the analogy it is necessary to assume that 

 in the case of Laminaria the effect of time is to increase the 

 concentration of the salts in the tissues. In this connection 

 Fenn also predicted that the changes in electrical resistance 

 offered by the gelatine, as the salt concentration is increased, 

 will give curves which are also similar to those of Osterhout's. 

 The experiments which the writer will now describe were under- 

 taken to test the truth of Fenn's prediction, namely, that the 

 electrical resistance of the gelatine' is greatest at the isoelectric 

 point, where the least alcohol is needed for precipitation. 



Method 



The gelatine used was one of the best commercial brands but 

 proved rather unsatisfactory because of the unavoidable high 

 electrolyte content. In a 1.5% solution the gelatine gave a 

 specific conductivity twenty times as great as once distilled 

 water, which had a specific conductivity of approximately 

 2 X 10-^. In practice a series of test tubes was prepared each 

 containing the gelatine solution plus the salt solution, the effect 

 of which was to be determined. For each tube was prepared a 

 control containing all the constituents with the exception of the 

 gelatine, for which distilled water was substituted. The specific 

 resistance was measured by means of the apparatus described in 

 the first part of this paper and the readings were corrected 



* Osterhout, W. J. V. The Permeability of Protoplasm to Ions and the 

 Theory of Antagonism. Science 35: 112. 1912. 



