REACTIONS OF ANIMALS. 85 



as nearly natural conditions as possible. With the exception of 

 Plethodon and Fontaria, they were kept only a few days. 



IV. EXPERIMENTAL RESULTS. 

 i. Dry Air. 



The air used in the experiments was dried in the sulphuric 

 acid filters described on page 82. The water vapor present 

 after treatment depended upon the humidity of the original air, 

 upon the temperature, the rate of flow, and the number of filters 

 used. On account of variations in temperature and relative 

 humidity from day to day, it is necessary to either practically 

 saturate all the air with water vapor or to dry all of it and follow 

 by standard treatment at a constant temperature if the same con- 

 ditions are to be produced from day to day. Tables I. and II. 

 (pp. 88, 96) show from 0.5 to 1.05 c.c. evaporation for 2O-minute 

 periods (calculated from lo-minute exposures) and relative humid- 

 ity of 9 to 20 per cent, for the treated air. The relative humidity 

 of the air used ranged from 40 to 60 per cent, of saturation; the 

 reduction in per cent, of humidity ranged from 34 to 52. The 

 moist air was more constant and the evaporation is arbitrarily 

 given as 0.02 c.c. per 20 minutes. This number is based upon a 

 number of one-hour exposures of the atmometers, as readable 

 results were not noted in lo-minute exposures. 



(a) Moist Forest Animals. 



i. Physiological Effect and Reactions. With the exception of 

 the snails the dry air was stimulating to all the animals tried. 

 Plethodon cinereus w T as stimulated at once in the driest air and 

 usually moved back and forth in the observation tubes. Activity 

 sometimes alternated with short periods of coiling but movement 

 was the rule and was usually increased during the first fifteen 

 minutes when erratic movements occurred. These were usually 

 followed by coiling or cessation of activity accompanying a dry 

 appearance of the skin. The animals usually dried and shriveled 

 without further activity, the ability to move being gradually 

 reduced. In the medium air, when the rate of evaporation was 

 low, they often behaved quite normally for a few minutes when 



