PHYSIOLOGY. 



fcf the bile and urine, and often take up 

 even the colouring parts of the former, 

 and convey them into the blood, whence 

 they are deposited in all our organs, and 

 produce the yellowness of jaundice. 

 They introduce various diseases into the 

 human frame, as syphilis, hydrophobia, 

 inoculated small-pox, &c. ; and in other 

 instances act in a curative manner by tak- 

 ing up extravasated blood, by reducing 

 swollen parts, Sec. 



The circulation;, is the motion by which 

 the blood, setting out from the heart, is 

 constantly carried to all parts of the body 

 in the arteries, and returns to the same 

 point in the veins. The uses of this cir- 

 culatory motion are, to submit the blood 

 altered by the mixture of lymph and 

 chyle to the contact of the atmosphere 

 in the lungs (respiration), to convey it to 

 several organs in which various animal 

 fluids are separated from it, (secretion) ; 

 and to every part of the body, for sup- 



}j lying its growth and repairing its losses, 

 >y means of its nutritive particles when 

 completely assimilated (nutrition). The 

 conveyance or transport of our fluids, ra- 

 ther than their elaboration, is the office 

 of the organs of circulation. In this view 

 they may be compared to those labour- 

 ers, who in a large manufactory, from 

 which various products issue, carry the 

 materials to the workmen employed in 

 the actual fabrication. As among the lat- 

 ter there are some who purify and bring 

 to perfection the materials furnished by 

 others, so the lungs and secretory glands 

 are constantly employed in separating 

 from the blood all those heterogenous 

 matters which could not be assimilated to 

 the substance of our organs. 



The word circulation, when used abso- 

 lutely, comprehends the whole course of 

 the blood, as well in the lungs, as in the 

 arteries and veins of the body at large. 

 The greater circulation is the passage of 

 the blood from the left side of the heart, 

 through the arteries, to the extremities 

 of the body, and its return through the 

 veins to the right side of the same viscus. 

 The lesser circulation is the transmission 

 of the blood from the right to the left 

 side of the heart, through the lungs. 



The course, which the blood takes, has 

 been already explained in the article 

 A.XATOMT. We subjoin the proofs and ex- 

 periments, by which the facts there stat- 

 ed are supported. 



The passage of the blood through the 

 heart, z. e. from the right auricle to the 

 left ventricle, by the medium of the lungs, 

 is manifest from the structure of the 



VOL. V. 



heart itself. The valves, which are plac- 

 ed at its various apertures, actually will 

 not admit of the blood's motion in any 

 other direction than what we have des- 

 cribed. That this fluid passes from the 

 heart into the trunk of the aorta, thence 

 into its branches, and so on to the most 

 minute ramifications, is evinced; 1. By 

 the effect of ligatures on these vessels ; 

 the artery becomes turgid between the 

 heart and the ligature, and empty be- 

 tween the ligature and its distribution. 

 2. By opening an artery when tied, above, 

 and below the ligature ; the blood in this 

 case flows from that opening only, which 

 is nearest to the heart. 3. By ocular 

 testimony ; the passage of the blood can 

 be seen with the aid of glasses in frogs, 

 fishes, &c. The passage of the blo'od 

 through the veins, in a contrary course to 

 that in which it ilows along the arteries, 

 z. e. from the minute nullifications towards 

 the trunks, and thence to the heart, is 

 proved. 1. By the structure and dispo- 

 sition of the valves, which afford an invin- 

 cible impediment to all retrograde motions 

 2. By ligatures on these vessels, which 

 make the vein turgid between the extre- 

 mities of the body and the ligature, and 

 empty in the rest of its course. 3. Ufc 

 opening a vein, when tied, above and b<?* 

 low the ligature. 4. By microscopical ob- 

 servation in animals. 



The passage of the blood from the ar- 

 teries into the veins seems to flow as a 

 corollory, from what we have stated con- 

 cerning the proofs of its course in these 

 two systems of vessels. We have shewn 

 that the ultimate ai'teries are continuous 

 with the origins of the veins ; that the 

 blo'od moves from the heart to the extre- 

 mities in the former vessels, and that it 

 passes from the extremities to the heart 

 In the latter. The intermediate passage is 

 a direct consequence of these facts. But 

 it may be demonstrated by direct proofs 

 independently of this argument. If we tie 

 the artery of a part, its correspondent 

 vein receives no blood ; if we take off the 

 ligature the vein is again filled. The 

 quantity of blood expelled from the aor- 

 tic ventricle is so considerable, that the 

 supply can only be kept up by its return 

 to the heart. We calculate that two 

 ounces are sent into the aorta at each pul- 

 sation ; if we suppose 80 pulsations in a 

 minute, 9,600 ounces will be thrown out 

 in an hour ; and 14,400 pounds in a day. 

 The same blood, therefore, which the 

 aorta received from the heart, must be 

 returned to this yiscus; and the only pas- 

 sage, by which it can return, is through 



Yy ' 



