Effects of Desiccation on the Rotifer 



245 



larger number of deaths in the longer period of drying. Is there 

 a gradual loss of water which eventually injures the animals ? 

 Does slow metabolism gradually destroy the organs of the body 

 in the absence of food ? Do injurious waste products accumulate 

 which cannot be eliminated ? Or do changes of temperature 

 and moisture result in mechanical injury to the tissues ? 



That changes in moisture and changes in temperature insofar 

 as they cause changes in the relative humidity of the atmosphere 

 have an injurious effect may easily be shown. In the following 

 experiments two dishes containing rotifers from the same culture 

 were dried under exactly the same conditions, no sand being 

 present in either. Both were placed in an oven at a temperature 

 of 40°. The first one was kept covered, its condition, therefore, 

 remaining uniform, and the second one alternately turned upside 

 down over a small dish of water and right side up over the same 

 dish, being thus exposed to alternating moist and dry conditions. 

 This process was repeated five times during a period of an hour 

 and a half. In no case were the rotifers touched by the water. 

 As in the other experiments the time required for the appearance 

 of movements and the percentage that recovered were noted. 



TABLE VIII 



Efect of alternations of moisture and dryness 



This experiment is interesting in several ways. In the first 

 place, if death depended on loss of water as assumed by Davis 

 and others w^e should expect the mortality to be less in the second 

 case in which the rotifers had scarcely an opportunity to become 

 thoroughly dried than in the first in which evaporation was un- 

 checked. Instead, we find the reverse to be the case. In the 

 second place the experiment shows in a phyical way watsiologh 



