382 LOUIS MAX HICKERNELL. 



material in question until actual charring takes place. It is 

 evident, therefore, that the absolute desiccation of living sub- 

 stance cannot be accomplished by means of heat without de- 

 stroying life. On the other hand, the second method of desic- 

 cation mentioned above will not remove the last trace of chemi- 

 cally combined water from living tissue. Since an absolute 

 desiccation of living things without the destruction of life is 

 impossible by the second method it seems certain that no rotifer 

 or other living thing has ever lived after an absolute desiccation. 



The recorded observations upon the desiccation of living things, 

 whether animal or plant, have to do with a relative rather than 

 with an absolute desiccation. If the water content is lowered 

 much below the normal percentage the organism may be said 

 to have undergone an actual or even a complete desiccation but 

 it will be understood that in all cases this does not imply that the 

 condition of dryness is absolute. 



Water may be acquired by an organism in three ways: (i) It 

 may be imbibed directly; (2) it may be taken in with solid food, 

 and (3) it may be formed within the organism by metabolic 

 changes in the organic constituents of the food and tissues 

 induced by respiration and other vital processes! 



Imbibed water probably makes up the greater part of the 

 cell-sap. Its method of combination with the living substance 

 may be, as Nageli contended, not chemical but a mere physical 

 attraction due to minute molecular aggregations designated as 

 micellae, between which the water enters by capillary attraction 

 and forcing the micellae apart increases the volume of the tissues. 

 On the other hand, as Babcock points out, all of the phenomena 

 of imbibition point directly to a molecular combination between 

 the substance composing an organized body and water. The 

 combination is in most cases feeble, since it is broken up by a 

 relatively low temperature without changing the molecular 

 structure of either the solid tissue or the water. It is however 

 analogous to the behavior of many substances, both organic 

 and inorganic, w T hich crystallize with water of crystallization. 



The water taken in with solid food probably has in part the 

 same fate as imbibed water although its history is slightly 

 different. In Philodina the distinction between these two 



