on the Vitality of Animals* 5 



sects would be very convenient for my experiments, because, 

 as it was necessary that they should be comparative, I should 

 thus be enabled to try several animals at the same time and 

 under a similarity of circumstances. 



The first which I tried were caterpillars of the phalcema 

 -chrysolea. The most favourable temperature for these ani- 

 mals is between -f 10 and 4- 20 *, and the further it is di- 

 stant from temperate the less vivaceous they are, till they 

 become entirely torpid at 4- 2, Q, &c. I took twelve of 

 the most lively of a multitude of these caterpillars and made 

 them pass from the temperature of 4- 5°, at which they 

 were, to that of 4- 2°, G and — 2°, always leaving the 

 space of a quarter of an hour between each temperature. 

 Having left them at -f- 2* for four hours, I brought them, 

 in equal spaces of time, to 4- 16°, in order to excite them 

 to life: but my attempt was fruitless, since the heat of the 

 fire was not able to produce in them any vital motion. 



But as my phalaenaj were killed by a slow passage -from 

 iieat to cold, it was necessary to examine what would be 

 the case by a rapid transition. For thia purpose I conveyed 

 tweive other caterpillars, as lively as the former, from a 

 ;place the temperature of which was 4- 5° to another where 

 it rose to -f 7 ., in order to render more sensible the rapid 

 passage to that to which I intended to make them descend. 

 I then took the small phial in w*hieh they were and im- 

 mersed it suddenly in pounded ice at — 2°. Having left 

 them in this state for lour hours, I gradually raised the 

 small phial, in which they remained completely torpid, to 

 the temperature of + 16°, at which they gave signs of life. 



I repeated these experiments on other caterpillars with 

 results entirely similar. I at length made the same experi- 

 ments on spiders ; but as they are much less sensible of 

 cold, it was necessary to keep them a longer time in a cold 

 temperature. The results, however, were similar to those 

 given me by caterpillars. 



Sometimes I raised the temperature of -the spiders to 

 4- 30°, at which they were exceedingly lively, and then 

 threw them speedily into phials immersed to the neck in 

 pounded ice. I always observed that these spidc rs returned 

 -sooner to life than those which passed as speedilv to cold, 

 but which had proceeded from a temperature much lower. 



It was therefore sufficiently confirmed that these animals 

 were more injured by being slowly rather than rapidly de- 

 prived of caloric. But it was of importance to ascertain what 



* Probably Reaumur's thermometer is intended. 



A 3 would 



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