'202 AITIMALCULA OF INFUSIONS. J* 



.higher orders, I perceive, I fay, that thefe ani- 

 malcula cannot expand at 174°, but want of 

 /time prevented the extenfion of your refearches 

 on this point. It would be very defirable to as- 

 certain the degree, or to come near it, at which 

 ■they maybe developed(i); and it would be ufe- 

 ful to afcertain how much cold they can fuftain. 

 All this would have fome tendency to elucidate 

 the fmgular conflitution of thefe living beings, 

 and afford us comparifons and indudions which 

 might throw fome light on fo obfcure a part 

 of the animal kingdom. The evolution of ani- 

 mals is evidently proportioned to the heat necef- 

 fary for putting their fluids in motion, and for 

 extenfion of their velTels. The earlieft plants 

 are apparently thofe whofe liquids are put in mo- 

 tion by the leaft degree of heat, and whofe vef- 

 fels afford but little rcfiflance to gentle impref- 

 lions of their fluids. The life of many infefts 

 may be abridged or prolonged by keeping them 

 in cold or warm fituations, Corps Organises, Art, 

 167 ; and we know there are infefts that can 

 fupport the cold of 14 or 15*^ of Reaumur's 

 thermometer, and remain alive though complete- 



(i) By experiments afterwards inftituted, I was iuble 

 £• fix the precife degree. 



