232 H. DAVIS ON THE SO-CALLED DESICCATION OF ROTIFERS. 



be revived. Then there was the incredulous party, who denied some 

 things stated by their opponents, and vainly tried to explain others. 



In 1872 the balance of evidence so far favoured what may be 

 called the dry-and-immortal theory, that the standard text books — 

 in England at least — summed up entirely in its favour. Dr. 

 Carpenter, in his " Microscope and its Revelations," said, when 

 speaking of Rotifers and Tardigrades, " they can be reduced to a 

 most complete state of dryness, kept in this condition for any length 

 oj time, and revive on being moistened. . . . Individuals have been 

 kept in a vacuum with sulphuric acid and chloride of calcium (thus 

 suffering the most complete desiccation the chemist can effect) and 

 yet have not lost their capability of revivification." Pritchard 

 taught exactly the same lesson. 



About this time, however, G. H. Lewes, in his " Studies of 

 Animal Life," made out a fair case for the other side. He did not 

 indeed advance anything absolutely new, but his clear common- 

 sense arguments toldcrushingly against the common fallacy, and led 

 him very near to a full explanation of all the undoubted facts. His 

 belief — like that of Spallanzani before him — was that sand and 

 dirt formed a perfect protection against the absorptive and drying 

 effects of a vacuum and of heat, and had found that Rotifers, when 

 naturally dried on a glass-slip without dirt, never revived, therefore 

 dirt was somehow the preservative. 



I, for one, not being satisfied with the dirt theory, went carefully 

 over all the experiments I could read of, having a good stock of 

 material, mainly P. roseola?. I found that they certainly could be 

 revived after being heated to 200° (Fah.), and that some survived 

 a week's confinement in the vacuum of an excellent air-pump with 

 sulphuric acid. 



Rotifers treated as described were then picked out with a pencil 

 and crushed between two glasses under the microscope, when some 

 of these Rotifers (which had undergone " the most complete 

 desiccation the chemist could effect") distinctly emitted their con- 

 tained fluids, and the certainty was apparent that the desiccating 

 power of the air-pump had been over-rated. It occurred to me that 

 Rotifers generally being slimy, their gelatinous secretion might, on 

 their drying, coat these Philodines all over, and form a strong 

 shell, proof against the air-pump and the ineffective chemist. Some 

 grapes were then thinly coated with good glue, and as these were 

 found to bear the air-pump with acid without fracture or internal 

 drying, it was but a fair inference that the Rotifers, if similarly 



