194 HOMER E. CHENOWETH. 



About thirty experiments were performed to test the reactions 

 of these mice to the different evaporating powers of the air. 

 The preceding graphs of a few of the experiments will serve to 

 show the general behavior of these mice in all the experiments. 



In Experiment 10, Chart I., the moisteners were becoming very 

 dry and the filters were weak; both were renewed in Experiment 

 II. The standard rate of flow, 27 liters per minute, was used in 

 both experiments. The mouse was always placed in the division 

 of the cage where evaporation was the lowest. In Experiment 

 10 the mouse moved directly to the opposite end of the cage where 

 the rate of evaporation was the highest and remained there ten 

 minutes. It behaved quite normally for five minutes, then it 

 grew restless and kept turning around in the corner of the cage; 

 several times it stretched and lay flat and yawned. After moving 

 back to the division of lowest evaporation it made three trips 

 across the cage but the period spent in the dry air was less each 

 time. The threshold of stimulation was lowered each time so that 

 finally the mouse oriented directly, and returned to the air of 

 low evaporation. Theoughout the rest of the experiment it 

 remained there and behaved normally. Thirty minutes after 

 the experiment was closed the mouse was still in the same division 

 of the cage. In Experiment n the mouse reacted much more 

 definitely, due in part no doubt to the air of higher evaporation 

 and the physiological state of the animal. It remained in the air 

 of lowest evaporation throughout the experiment excepting when 

 it was forced out. A marked negative reaction to the highest 

 evaporation is clear in both experiments. 



The rate of flow influences the rate of evaporation in a marked 

 degree. The mice oriented directly in most cases to a very small 

 change in the rate of flow, but I am inclined to attribute this 

 orientation more as a response to a mechanical stimulation; 

 however the higher rate of evaporation was no doubt a factor in 

 determining this response. In their natural environment changes 

 in wind velocity would directly influence their behavior though 

 these variations are very slight in the forest. In their under- 

 ground burrows it would have little or no effect. The differences 

 in wind velocity existing between the forest and the prairie no 

 doubt play an important role in restricting their habitats to the 



