251 
which were placed in vaciw, though the reverse uni- 
formly happened, when the receiver contained a cer- 
tain quantity of air. If, however, infusions, contain- 
ing animalcules, were placed under the exhausted re- 
ceiver, the animalcules lived many days, but perished 
long before others of the same kind, which were, 
kept in the open air *. It may be doubted, how- 
ever, whether the vacuum was in these experiments 
rendered perfect; for Dr Hooke found, that, when a 
quantity of vinegar, replete with eels, was included 
in a small phial, and stopped very close, all the in- 
cluded animals in a very short time died, as if they 
had been stilled ! The specific change effected in. 
the air, by the respiration of this class of animals, 
may be inferred from the experiments of Mr Davy, 
who found (52.) that zoophytes not only require 
the presence of air in the water in which they live, 
but act upon it like fishes, that is, convert its oxy- 
gen gas into carbonic acid. 
537. In the class Vermes, which falls next to be 
noticed in the order of our present arrangement, the 
first experiments, which we have met with, were 
made by the celebrated Scheele. He kept some 
leeches in a closed phial, which was half filled with 
water, and half with air, till they died. He then 
examined the air. It had no peculiar smell, but it 
extinguished the flame of a candle. These animals 
he found would live two years in the same water, 
when it had a free communication with the air ; but 
* Tracts, &c. p. 42. 
t Micrograpliiu, p. 2 I/. 
