638 



CIRCULATION. 



in Abhandl. der k'dnigl. Akad. der Wissensch. zu 

 Berlin fur 1816-1817. *Gruithuisen, in Salzh. Med. 

 Chir. Zeituug, 1818, Bd iv. ; Nov. Act. Acad. 

 Caes. Leop. vol. x. G. R. Treviranus, Vermischte 

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 bedingungen dcr weiss-und kaltbluetigeu Thiere, 

 4to. Leipz. 1824 ; Nov. Act. Ac. Caes. Leop. 

 vols. xiii. and xvi. Fleming, in Mem. of Wer- 

 iierian Society, vol. iv. *Huschke, in Isis for 

 1826. *R. Grant, in Edin. Phil. Journal, Edin. 

 New Phil. Journ., Edin. Journal of Science, and 

 Trans, of Zoological Society. Sir E. Home, Phil. 

 Trans. 1827. *Raspail, Mem. de la Soc. d'Hist. 

 Nat. de Paris, 4to. vol. iv. 1827 ; Chimie Or- 

 ganique, 8vo. Paris, 1833. Meyen, Isis for 1828. 

 E. H. Weber, in Meckel's Archiv. 1828. Fr. Esch- 

 scholz, System der Acalephen, 4tn. Berlin, 1829. 

 Dutrochet, in Annales des Sc. Nat. t. xv. 1828. 

 *W. Sharpey, in Edin. Med. and Surg. Journal, 

 vol. xxxiv. July, 1830. Guillot, in Magendie 

 Journal de Physiologic, xi. 1831. *Eltrenberg, 

 Ueber Infusorien, in Abhandl. der k. Acad. der 

 Wissensch. zu Berlin fur 1830 and 1831, Muller's 

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 Mutter, Handbuch der Physiologic, Bd i. 8vo. 

 1833. H. Rathke, in Dorpater Jahrbucher, &c. 

 Bd i. 1833. *Jo$. J. Lister, in Phil. Trans. 1834. 

 *J. E. Purkinje fy G. Valentin, in Muller's Archiw. 

 Bd i. translated in Dublin Journ. of Med. and 

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 Phil. Journ. vol. xix. July, 1835; also, by the 

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 1835, (the only systematic treatise on the subject.) 



( W. Sharpey.) 



CIRCULATION (in Physiology), (Circu- 

 latio, Circulus, Circuitus Sanguinis ; Fr. Cir- 

 culation du Sang; Germ. Blutlauf; Ital. Cir- 

 colazione del Sangue;) designates in its more 

 extensive signification the course through or- 

 ganised beings of their nutritious fluid; as 

 limited to man and the higher orders of ani- 

 mals, the course of the blood from the heart 

 to the most minute vessels, and from these back 

 to the heart. 



By modern writers on physiology the circu- 

 lation of the blood is generally included under 

 the nutritive functions, because one of the most 

 important purposes served by the motion of 

 this fluid through the various textures and 

 organs of the body is the supply of those new 

 ingredients which are necessary to carry on the 

 process of growth and the changes of nu- 

 trition. A very slight acquaintance with ani- 

 mal physiology teaches us, however, that the 

 function of circulation has another very im- 

 portant and immediate use, viz, the support 

 of that condition of the textures and organs 

 which is necessary to enable them to exercise 

 their vital properties. It was on account of 

 the apparent necessity of a constant supply of 

 blood for the support of the animal powers, 

 that Galen placed circulation, along with re- 

 spiration, among the vital functions. 



In the following article it is intended to de- 

 scribe more particularly the course of the 

 blood in the human body and the powers by 

 which it is moved, and also to state the general 

 facts ascertained regarding the function of cir- 

 culation in other animals. 



For the sake of clearness it will be neces- 

 sary to divide the subject into several de 



partments. The first, of these will compre- 

 hend a description of the course of the blood 

 in man; the second of its course in animals. 

 In the third will be considered the phenomena 

 presented by the blood during its motion, the 

 properties of the organs in which it circulates, 

 and the powers by which it is propelled ; and 

 in the fourth will be mentioned the more im- 

 portant circumstances connected with the other 

 functions which modify the circulation. 



The term circulation applied by its cele- 

 brated discoverer, Harvey, to the motion of the 

 blood, is sufficiently expressive of the general fact 

 that this fluid, or the greater part of it at least, 

 in being carried through the body, moves in a 

 circular course, or, that in performing its jour- 

 ney through the body, the blood always re- 

 turns to the same place from which it set out. 

 The term is equally applicable to the func- 

 tion by which a supply of nutritious fluids is 

 kept up in the lowest animals, in which a pro- 

 gressive motion of a fluid of the nature of 

 blood takes place, as well as in the highest ; for 

 in nearly the whole of them there is a central 

 part of the circulatory organs, which forms the 

 rallying point, as it were, of the rest, -from 

 which the blood begins its course and to which 

 it is brought back, in a longer or shorter period 

 of time, after having passed through the dif- 

 ferent organized parts. 



I. COURSE OF THE BLOOD IN MAN. 



The organs of circulation consist of the heart, 

 arteries, veins, and capillary vessels. We refer the 

 reader to the articles on these different organs for 

 all details relative to their anatomical structure. 



In man and warm-blooded animals there 

 are two passages through the interior of the 

 heart, through each of which a stream of blood 

 is propelled at the same time, so that the heart 

 is alternately receiving and giving out a certain 

 quantity of blood upon each side. 



The two auricles serve as receiving cavities 

 for the blood which is constantly flowing into 

 the heart from the veins or those vessels which 

 have the office of returning blood to the centre 

 of the circulation. By the contraction of the 

 muscular parietes of the auricles, the blood is 

 propelled from these cavities into the ventricles, 

 which, in their turn, contract with force and 

 thus propel their contents into the arteries, or 

 those vessels which serve to transmit blood 

 outwards from the centre of the circulatory 

 organs. The auricles and ventricles of the 

 opposite sides acting simultaneously, and the 

 size of these cavities on the right and left sides 

 of the heart being nearly equal, the quantity 

 of blood which is made to pass through each 

 of them at one and the same time must also be 

 nearly equal. 



The cavities on the left side of the heart are 

 adapted to propel the blood into those arteries 

 which are subservient to the nutrition of the 

 body, while those on the right side of the heart 

 send the blood to the lungs for the purposes 

 of respiration. The construction of the heart 

 and the connection of its parts with the arte- 

 ries and veins are such that the whole of that 



