Microscopical Essays. 



459 



If the fmalled drop of urine is put into a drop of water, where 

 thefe animalcula are roving about, apparently happy and eafy, 

 they inftantly fly to the other fide, but the acid foon communi- 

 cating itfelf to this part, their druggies to efcape are increafed, 

 but the evil alfo increafmg, they are thrown into convulfions/ and 

 foon expire. 



Among animalcula, as in every other part of nature, there is 

 always a certain proportion p refer ved between the fize of the in- 

 dividuals and their number. There are always fewed amongft the 

 larger kinds, but they increafe in number as they diminish in fize, 

 till of the lafl or lowed to which our powers of magnifying will 

 reach, there are myriads to one of the larger. Like other ani- 

 mals, they increafe in fize from their birth till they have attained 

 their full growth. When deprived of food, they grow thin and 

 perilh, and different degrees of organization are to be difcovered 

 in their dru&ure. 



The birth and propagation of thefe microfcopic beings is as 

 regular as that of the largeft animals of our globe ; for though 

 their extreme minutenefs prevents us, in mod cafes, from feeing 

 the germ from which they fpring, yet we are well aflured, from 

 numerous obfervations, that the manner in which they multiply is 

 regulated by conftant and invariable laws. 



We have feen that different fpecies of the hydra and vorticella 

 multiply and increafe by natural divifions and fubdivifions of the 

 parent's body ; this manner of propagation is very common among 

 the animalcula in infufions, though with many remarkable va- 

 rieties. Some multiply by a tranfverfe divifion, a contraction 



3 K 2 takes 



