186 OF THE HEART, VESSELS 



bled the refe mlrabih of the carotid artery of the herbivofoni 

 qiiadriiped, But a nearer vieNY' will UDdeceiye iis, For I have 

 foiind, that, hy eiegant fnbdiviiions and folds of the mem- 

 brane of the-gills, their furface, in a large fkate, is nearly 

 cqual to the whole external furface of the human body^ 



7. Thus in each fide of the body of a (kate there arc four 

 double gllls , or giils \y'ith two fides each, and one fingle gill; 

 or tliere are in ali eighteen fides or furfaces, on which the 

 branchial artery is fpread out» On each of thefe lides there are 

 about 50 divifions, or doubiings of thc membrane of thc 

 gills (^). Each divifion has on each fide of it 160 fubdivi- 

 fions, doublings, or folds of its membrane; the length cA 

 cach of which in a very large fl<:ate is about one-eighth of an 

 inch , and its breadth about one-fixteenth of an incb (/). So 

 that in the whole gills there are 1 44,000 fnbdivifions, or folds, 

 the two fides of each of "which are equal to the G^th part of a 

 fquare inch, or the furface of the whole gills in a large fkatc 

 is equal to 2250 fquare inches, that is, to more than i 5 fqua- 

 re feet, which have becn fuppofed equal to the whoie ex- 

 ternal furface of the human body. When afier a good inje<fl-« 

 ion of the artery, a microfcope is applied, the whole extent 

 of the membrane of the gilis is feen covered with a beautiful 

 iiet-work of exceedingly minute veffels» 



g. As fishes taint the water they refpire, in nearly the 

 feme manner as we taint the air we breathe, it appears thj^t 

 fome matter, either ufeiefs or hurtful, or f)oth , is carried off 

 from their biood as it paffes through thcir giils» 



9. When difiillcd oil of turpentine , coloured with 

 vcrmilion, is injeded with moderate force into the branch- 

 lal artery of a living or recently dead fkate, fome of the co- 

 lourlefs part of the oil exfudes upon tlie furface of iht gills, 



But 



{e) See Tab. I. %, la. 

 (/) Tab. l. fig, 3, 



