EFFECTS OF STRYCHNINE UPON RATE OF LEARNING 143 



problem. Accumulating evidence of the dependence of the 

 direction of nerve conduction upon the relative refractory 

 phases of the neurons involved (Forbes and Gregg/ 15) and the 

 growing acceptance of the all-or-none law of nerve action make 

 it seem less and less probable that any of the current accounts 

 of the neurological basis of habit is in any way adequate to ac- 

 count for the facts. The presentation of the problem in this 

 form has nevertheless seemed of value in spite of the possible 

 falsity of all the hypotheses which it is designed to test, if only 

 as a means of emphasizing the strictly physiological nature of 

 the problem of learning and the necessity for a more concrete 

 formulation of this problem than has hitherto been made. 



METHODS IN THE PRESENT EXPERIMENTS 



For testing the effects of the central excitants, albino rats, 

 approximately sixty-five days old, were used. They were 

 trained in the circular graphic maze (Watson, '14 b), time, 

 distance, errors, and number of trials required for learning being 

 recorded. The technique of training was essentially that de- 

 scribed by Hubbert ('15) with the difference that each animal 

 was given five trials per day and that the training was continued 

 until three successive errorless trials were made during one day's 

 practice. 



Administration of drug. The drugs given were strychnine 

 sulphate (Powers and Weightman) and caffeine (pure alkaloid, 

 Merck) in aqueous solution. They were injected subcutane- 

 ously in solutions of such strength that 0.10 cc. contained the 

 desired dose. The minimum lethal dose of strychnine for an 

 150 gram rat was determined at the beginning of the experi- 

 ments as about 0.50 mgm. This is usually fatal in about fifteen 

 minutes but its effect varies somewhat with the concentration 

 of the solution and with individual differences in the animals, 

 one rat being killed by 0.10 mgm., others surviving 0.50 mgm. 

 without convulsions. For study, two concentrations of the 

 drug were used, 0.10 mgm. and 0.05 mgm. per 0.10 cc. of solu- 

 tion. These correspond by weight to doses of about 0.8 and 0.4 



