642 



SPECIAL PHYSIOLOGY. 



He founded his conclusions, first, on the anatomical connections and 

 continuity of the heart, arteries, and veins; secondly, on the facts, 

 that on dividing an artery, blood issues from that end which is still 

 connected with the heart, whilst on dividing a vein, the blood comes 

 from the end furthest from the heart; thirdly, on the fact that a vein, 

 when tied, swells on the side of the ligature furthest from the heart ; 

 and lastly, on the direction of the valves in the veins, and of those 



Fig. 108. 



Fig. 108 Diagram of the cavities on the two sides of the heart, to show the course of the blood through 

 it. 1, Vena cava superior; 2, vena cava inferior; 3, right auricle; 4, right ventricle; 5, pulmonary artery; 

 6, 6, pulmonary veins, right and left ; 7, left auricle ; 8. left ventricle ; 9, aorta ; 10, hepatic veins. The dark 

 parts are those which contain venous blood ; the light parts contain arterial blood. The arrows indicate 

 the course of the blood within the heart, and through the lungs and the body. Thus, the dark blood 

 returns from the upper half of the body by the superior vena cava. 1, and from the lower half of the body 

 by the inferior vena cava, 2, joined by the hepatic veins, 10; it enters the right auricle, 3, passes into the 

 right ventricle, 4, and then through the pulmonary artery, 5, and it branches through the cnpillaries of 

 both lungs. Here, it is changed into red blood ; gathered then into the pulmonary veins, 6, 6, it enters the 

 left auricle, 7, passes into the left ventricle, 8. and thence through the aorta, 9, and its branches, into the 

 capillaries of all parts of the body. Here it again becomes dark, and is once more returned by the venas 

 cavae, 1, 2, to the right side of the heart. It is seen that the right and left sides of the heart do not com- 

 municate. The one always contains dark, the other red blood. 



situated in the heart itself. Afterwards, the mode in which the blood 

 passes from the arteries into the veins, not quite understood by Harvey, 

 was explained by Malpighi's discovery of the capillary vessels, in the 

 frog's foot, in 1661. 



The proofs of the circulation of the blood, now usually advanced, 

 are identical with those just mentioned, viz., the anatomical connec- 

 tion and continuity of the heart, arteries, capillaries, and veins ; the 

 different direction in which the blood escapes from a cut artery and 

 a cut vein ; the effect of ligature upon the veins ; the special direction 

 of the valves of the heart and veins ; and lastly, the actual observa- 

 tion of the blood moving in the capillary vessels of the transparent 

 parts of animals, such as the translucent bodies of the larvae, or 

 young, of Amphibia and Fishes, the gills of the tadpole, the web of 

 the frog's foot, the mesentery of the mouse, the wing of the bat, and 

 even the retinae of our own eyes. 



