416 JOHN LINCK ULRICH 



tone of the extensor thrusts frequently occurred with a rise in 

 temperature and in humidity, and a slight but sudden fall in 

 temperature during the summer months after a hot spell had the 

 opposite effect, increasing the extensor tone of the limbs. This 

 increase in extensor tone might be expected to take place with a 

 lowering of temperature, for there is, as measured by the output 

 of carbon dioxide, and the intake of oxygen, a higher metabolic 

 rate at lower than at higher temperatures. Reflex stimulation of 

 the skin by reduced temperatures, in all probability, increases 

 this metabolic rate and the tonic reflexes are benefited thereby. 

 The reverse would be the case when the temperature is increased, 

 tonic reflexes would be diminished in strength, inclusive of the 

 extensor thrusts of the limbs. Sometimes when fluctuations oc- 

 curred in one member of a litter, they took place in other members 

 of the litter. Members of other litters revealed but the custom- 

 ary fluctuation in reflex thrusts. Possibly some litters are more 

 easily affected by changes in the environment than others. At 

 times it appears that fluctuation in certain limbs is characteristic 

 of one litter and not of others. At present it is difficult to state 

 what may condition fluctuations in one litter and not in another. 

 Sometimes the taking of food increases or decreases the extensor 

 tone of the thrusts. In some rats a variety of conditions pro- 

 duces fluctuations in these thrusts. These fluctuations will 

 presently be shown to condition variations in the behavior of 

 rats or in the methods of learning problems. 



Obviously, there exists one satisfactory evidence of Jennings' 

 (14) statement that there occurs, as a result of changes in the 

 environment, a change in the physiological state of an organism; 

 however, this state must not be regarded as something permanent 

 and static, but a change in the functional condition of the or- 

 ganism. Soon it will be evident that learning is not exactly a 

 ready resolution of the physiological state of an organism, but 

 is to be regarded as the facilitation, or, the more ready working 

 of an exaggerated performance of coordinated, integrated re- 

 flexes interacting with many other parts of the body. These 

 coordinated reflexes which solve the problem persist, because a 

 resolution takes place, which is essentially the development of 



