ii6 THE PHILOSOPHY 



motion. Were it poffible for man to move •with a fwiftnefs equal 

 to that of a fwallow, the refiftance of the air, as he is not provided 

 with internal refervoirs fimilar to thofe of birds, would Toon fuffo- 

 cate him. Neither does the difficulty he mentions, with regard to 

 the ftrudure of the oflrich, feem to contradia his theory; for 

 though, as formerly remarked, the oftrich does not fly, he runs with 

 aftonifhing rapidity. 



The refpiration of air is not only neceflary to the exiftence of 

 land-animals, but to that of fishes of every denomination. Coeta- 

 ceous fifhes, or thofe of the whale-kind, refpire, like man and qua- 

 drupeds, by means of lungs; and, of courfe, they are obliged, at 

 certain intervals, to come to the furface, in order to throw out the 

 former air, and to take in a frefb fupply. 



Inftead of lungs, the other fpecies of fillies are furnifhed with gills, 

 through which they refpire both water and air; for air is univerfal- 

 ]y difFufed or mixed with every portion of water. When a free 

 communication with the external air is prevented by ice, or by ar- 

 tifice, fifhes immediately difcover fymptoms of uneafmels, and foon 

 perilh. iElian informs us, that, in winter, when the river Ifter was 

 frozen, the fifhers dug holes in the ice ; that great numbers of fiOies 

 reforted to thefe holes ; and that their eagernefs was fo great, that 

 they allowed themfelves to be feized by the hands of the fifliermen^ 

 Rondeletius made many experiments on this fiibjed. If, fays he, 

 fifhes are put into a narrow- mouthed veffel filled with water, and 

 a communication with the air be preferved, the animals live, and 

 fwir^i about, not for days and months only, but for feveral years. 

 If the mouth of the vefiel, however, be fo clofely fliut, either with 

 the hand, or any other covering, that the pafiage of the air is ex- 

 cluded, the fiflies fuddenly die. Immediately after the mouth of 

 the veffel is clofed, the creatures rufh tumultuoufly, one above an- 

 other. 



