^■^4- ANIMALCULA OF INFUSIONS. lu 



merit repetition, extenfion, and variation, much 

 more than they have hitherto received j and here 

 you have done well. 



Excefs. of heat tends to deftroy the effential 

 quahties in the nutritive juices of the plant ; and 

 the alterations thence confequent are a natural 

 caufe of its death. Ancient philofophers would 

 have faid, extreme heat took away the radical hu- 

 midity of the plant ; and although the expreflion 

 is not ufed by the moderns, it is good fenfe. 



XI. Your experiments on mould have excited 

 my attention very much. When the vegetation 

 of thefe minute plants ceafes, in veflels hermeti- 

 cally fealed and expofed to the adion of heat, it 

 is more than probable that the numbers, which 

 appeared on vegetable fubftances that had boiled 

 from half an hour to two hours, came from the 

 ambient air. The feeds mud be of fuch extreme 

 minutenefs that we cannot wonder if they pene- 

 trate wherever air has accefs. Thefe vegetables, fo 

 very fmall, are, in the vegetable kingdom, what 

 animalcula are in the animal. Once, my dear 

 friend, 1 wrote to you how earned I was that 

 fome one fhould perfect the botanical microf- 

 cope. How many intercding fingularities would 

 it not prefent ? and how incomplete is it dill ? 

 We are acquainted with the large and the middle 

 fized vegetables. The rnod able botanids hav2 

 carefully defcribed the chief external parts. 



Th« 



