24 



atmosphere reanimates their powers and gives them 

 new energies. In the first case they are more feeble, 

 and their organs less susceptible of performing their 

 functions, than in the second ; and consequently these 

 animals will live longer in proportion as the consump- 

 tion of the oxygen is slower : as it has been demon- 

 strated that oxygen is necessary for their vitality in 

 the preceding experiments. 



Having proved in a satisfactory manner, that oxy- 

 gen is requisite for the existence of these worms, I 

 was induced next to ascertain what effect the gases 

 would have on them, that is improper for the respira- 

 tion of the more perfect animals. 



EXPERIMENT III. 



I obtained nitrogen ; by making a quantity of sul- 

 phur and iron filings into a paste with water, and pla- 

 ced the mixture in a plate over water, on a stand rai- 

 sed above the fluid, then inverted over it a bell-glass, 

 and allowed it to stand three or four days, by which 

 time an absorption of near a fifth had taken place. To 

 be satisfied that it was perfectly pure, I made a satu- 

 rated solution of the sulphuret of pot-ash, and washed 

 the nitrogen with it for some time. I filled the vessel 

 as before with mercury, and placed it on the shelf of 

 the apparatus, transmitted the nitrogen into the vessel, 

 and caused a number of worms to pass into it : they 

 first moved about with great activity, as if they suffer- 



