Effects of Desiccation on the Rotifer 



247 



equilibrium had been reached with more or less moist surround- 

 ing atmosphere. In a desiccator, to be sure, evaporation could 

 continue almost indefinitely, but it has been seen from the experi- 

 ments of Doyere, Gavarret, etc., that even after the most intense 

 desiccation possible by physical means at ordinary temperatures 

 many rotifers may recover, while they would surely have been 

 killed if kept long enough under conditions in which the same 

 degree of desiccation could never have been attained. Further- 

 more, in an atmosphere saturated with water vapor the drying 

 is very sHght and yet the same relation between mortality and dura- 

 tion of desiccation is noticed as in a case where thorough drying 

 may occur. All attempts made in the course of this work to show 

 by experiment that the intensity of desiccation in itself, and apart 

 from other factors, has an effect on the mortaUty gave negative 

 results. It could not be proved that an intense degree of desic- 

 cation is more injurious than a moderate one except insofar as a 

 greater mechanical injury results when the water is extracted rap- 

 idly from the tissues. Presumably, the harmful effect of very per- 

 fect desiccation would be but slight if the water could be extracted 

 slowly enough to avoid mechanical injury to the vital organs. 

 Indeed, it seems certain that under some conditions a complete 

 or nearly complete desiccation is far less harmful than an imper- 

 fect one. Rotifers kept in a moist atmosphere actually show a 

 greater mortality than those kept in a dry one. The following 

 experiment makes this point clear. Four dishes containing roti- 

 fers from the same culture were dried under exactly the same con- 

 ditions (40° C. and no sand). All were kept for four days, one 

 covered at room temperature, one covered at 40°, one in an atmos- 

 phere saturated with vapor at room temperature (average 20°) 

 and one similarly saturated at 40°. 



TABLE IX 



E^ect of moisture. Temperature constant (20°) 



