150 K. S. LASHLEY 



the group A and that the physiological effects were, on this 

 account, less. 



The dose of 0.05 mgm. had a much less pronounced effect on 

 the animals than the larger one. Except for an occasional 

 tremor they seemed in no wise different from those which had 

 not received the drug. 



Effects of the caffeine, in any quantity, were difficult to de- 

 tect. In general, its administration seemed to be followed by 

 some increase in timidity, exhibited in attempts to escape from 

 the experimenter's hands, to run out of the food compartment 

 of the maze at the experimeter's approach, and to hide in the 

 corners of the maze. This did not seem to be present after 

 the second or third day's practice. No tremor or inaccuracy of 

 movement was noted after injection of caffeine. 



There is some, though not very certain evidence of the es- 

 tablishment of tolerance to the drugs. After daily injections 

 for two weeks no symptoms were noted in any of the animals 

 following injections of 0.10 or even larger doses of strychnine, 

 and the animals receiving caffeine seemed normal in behavior. 



There were no deleterious after effects from the use of the 

 drugs. In some cases 0.10 mgm. of stryphnine was given daily 

 for three months. At the end of this time the animals were 

 well nourished and healthy. Practically all were mated, later, 

 and produced large healthy litters. 



THE INFLUENCE OF THE DRUGS UPON THE AMOUNT OF PRACTICE 

 REQUIRED FOR LEARNING 



Program of experiments. A preliminary experiment was 

 carried out upon four groups of animals receiving respectively 

 0.10 mgm. of strychnine, 0.05 mgm. of strychnine, 0.50 mgm. 

 of caffeine, and 0.10 cc. of distilled water. The animals were 

 trained until a record of three successive errorless runs was 

 reached, were then kept without practice for four weeks, and 

 were finally retrained without the drugs to test the retention 

 of the habit. When they were again able to thread the maze 

 without error, their speed and accuracy under the influence 



