162 



CHAP. XL 



THE MOTION OF THE BLOOD. 



' THE blood, to whose great and multifarious importance in 

 the system we have slightly alluded, is conveyed, with a few ex- 

 ceptions, into the most internal and extreme recesses. This is 

 proved by the minute injection of the vessels, and by the well- 

 known fact of blood issuing from almost every part on the 

 smallest scratch. 



" This red fluid does not, like an Euripus, ebb and flow in 

 the same vessels, as the ancients imagined, but pursues a circular 

 course ; so that, being propelled from the heart into the arteries, 

 it is distributed throughout the body, and returns again to the 

 heart through the veins. a 



" We shall, therefore, say something at present of the vessels 

 which contain the blood, and afterwards of the powers by which 

 they propel and receive it. 



" The vessels which receive the blood from the heart, and dis- 

 tribute it throughout the body, are termed arteries. 



" These are, upon the whole, less capacious than the veins ; 

 but in adult, and advanced age especially, of a texture far more 

 solid and compact, very elastic and strong. 



" The arteries consist of three coats b : 



" I. The exterior, called, by Haller, the TUNICA CELLULOSA 

 PROPRIA ; by others, the nervous, cartilaginous, tendinous, &c. 

 It is composed of condensed cellular membrane, externally more 

 lax, internally more and more compact : blood-vessels are seen 



a " Among warm-blooded animals, the egg, especially at the fourth and fifth 

 day of incubation, if placed under a simple microscope, such as the Lyonetian, 

 is most adapted for the demonstration of the circulation. 



Among frogs, the most proper is the equuleus of Lieberkiihn, described in the 

 Mdm. del'Acad. de Berlin, 1745." 



b " For the various opinions respecting the number and differences of the 

 arterial coats, consult, among others, Vine. Malacarne, Delia Osservat. in Chirurgia. 

 Turin, t. ii. p. 103. 



And C. Mondini, Opiiscoli sdentifici, t. i. Bologna, 1817. 4to. p. 161." 



