62 MOISTURE AND PROTOPLASM [Ch. II 



experiences. Many writers have assumed that this has been 

 rendered in their experiments very great or nearly perfect. 

 Thus DoYERE ('42, p. 28) says : " What is the condition of 

 the animalcules in the dried sand of the gutters? I have 

 never seen them, at such times, in any other condition than 

 reduced to spangles as fragile and more deformed than when 

 dried free on the glass. I have never discovered a single one 

 which manifested any traces whatever of life, or which did not 

 present all the appearances of a complete desiccation. Never- 

 theless, I do not pretend by this to invalidate all contrary asser- 

 tions ; the principal fact, that of the return to life after an 

 absolute desiccation, is not affected thereby." The physicist 

 Gavaeret ('59, p. 317) subjected, for 34 days, moss contain- 

 ing rotifers to a vacuum having a pressure of only 4 mm. of 

 mercury, and other experimenters have likewise employed a 

 similar "chemically drying" device, which they believed capa- 

 ble of extracting all water from the protoplasm. 



The evidence that all water is withdrawn from the body of 

 the organism is often very slight. The fact that the seeds or 

 plant tissues in which nematodes or tardigrades are living, 

 have been dried until they lose no appreciable weight, is not 

 sufficient evidence that their inhabitants are completely dried. 



On the other hand, there is positive evidence that one, at 

 least, of the organisms which has been considered as having 

 been absolutely dried, can protect itself from this condition. 

 It is especially Davis ('73) who has shown this. This author 

 has experimented with the rotifer Philodina roseata. When 

 dried on a glass plate with sand, it assumes a spherical form. 

 At the same time, however, it secretes a gelatinous envelope. 

 Thus encapsuled it may rest for days until upon the addition 

 of water it reassumes its active, adult form. That a layer 

 of such gelatinous substance is sufficient to resist the drying 

 action of a vacuum-chamber with sulphuric acid, was illus- 

 trated by putting grapes varnished with gelatine in such a dry 

 chamber for one week. They emerged in a fresh, juicy con- 

 dition. One of the encapsuled rotifers was crushed after 

 "desiccation" and yielded under the cover-glass a drop of fluid. 

 In this case then the rotifer was not fully dried. Davis 

 accounts for the fact that isolated rotifers dried on a clean 



