46 VICTOR E. SHELFORD 



clear, for while it doubtless causes a tendency to alkalinity, its 

 paralyzing effects are probably due to specific action upon the 

 protoplasm. It should be noted that alkalies, including am- 

 monia, as well as acids, usually excite animals and are almost as 

 potent as acids in causing reversal of reaction (Loeb, '06, Mast, 

 '11), increased irritability, etc. It appears then that a disturb- 

 ance of neutrality in either the direction of acidity or of alkalinity 

 may be expected to give such results as we have discovered in 

 connection with the reactions of fishes to gradients. The nega- 

 tive reactions here described are to conditions which can prim- 

 arily either dilute or concentrate the plasma either in the peri- 

 pheral sense organs or in the organism as a whole. Did this 

 result in acidity or in alkalinity or did it disturb some other 

 regulatory mechanism ? While a probable answer to this ques- 

 tion could be presented and discussed, we reserve it until special 

 investigation, now about to be undertaken, may have been com- 

 pleted. It is, however, more than probable that the increased 

 sensibility to air of high evaporating power is due to some dis- 

 turbance of neutrality, brought about by concentration. We 

 may note, also, that if associations are formed, they go hand in 

 hand with and can hardly be distinguished from the other type 

 of modification. In other words, there is no reason to assume 

 that associative memory is essentially different or stands 

 apart from the type of modification here described. In fact, it 

 appears that since all excitation and all activity increase the out- 

 put of carbon dioxide the neutrality mechanism may be involved 

 in all associative processes. Henderson ('13a) says it is gradually 

 becoming clear that all physico-chemical conditions in proto- 

 plasm — alkalinity, osmotic pressure, colloidal swelling, chemical 

 equilibrium, temperature — are interdependent and that car- 

 bonic acid and acid base equilibrium are among all these things 

 probably the most important variable. 



Thus it seems probable that many of the simpler problems 

 of associative memory must be referred to the biochemist for 

 solution. The zoologist and the psychologist can by their 

 present methods do little more than describe the phenomena of 

 modification and the best results can come only from general 

 cooperation. The need for cooperation between the psychologist 

 and the naturalist is even more evident than between psycho- 

 logist and biochemist. 



