RESPIRATION. 291 



considerable time without nourishment, but all 

 speedily perishing when deprived of air. The 

 influence of this element is requisite as well for 

 the production and developement, as for the con- 

 tinuance of organized beings in a living state. 

 No vegetable seed will germinate, nor will any 

 egg, even of the smallest insect, give birth to a 

 larva, if kept in a perfect vacuum. Experiments 

 on this subject have been varied and multiplied 

 without end by Spallanzani, who found that 

 insects under an air pump, confined in rarefied 

 air, in general lived for shorter periods in pro- 

 portion to the degree to which the exhaustion of 

 air had been carried. Those species of infu- 

 soria, which are most tenacious of life, lived in 

 very rarefied air for above a month : others 

 perished in fourteen, eleven, or eight days; and 

 some in two days only. In this imperfect 

 vacuum, they were seen still to continue their 

 accustomed evolutions, wheeling in circles, dart- 

 ing to the surface, or diving to the bottom of the 

 fluid, and producing vortices by the rapid vibra- 

 tion of their cilia, to catch the floating particles 

 which serve as their food : in course of time, 

 however, they invariably gave indications of un- 

 easiness ; their movements became languid, a 

 general relaxation ensued, and they at length 

 expired. But when the vacuum was rendered 

 perfect, none of the infusions of animal or vege- 

 table substances, which, under ordinary circum- 



