THE CAPILLARY VESSELS. 5 



with furious speed, crimsoning the face with hot blushes ; or another cause the vital 

 fluid to recoil to the heart, leaving the countenance pallid, the eyes vacant, and the 

 limbs cold and powerless, as if the very life had departed from the body. 



Not without reason do the earlier Scriptures speak so reverently of the blood, accept- 

 ing the outpoured life of beasts as an atonement for the sin, and witness of the peni- 

 tence of man, and forbid its use for any less sacred office. Nor was it without a still 

 mightier meaning that the later Scriptures endue the blood with a sacramental sense, 

 giving even to its vegetable symbol, the blood of the grape, a dignity greater than that 

 of the former sacrifices; 



A few words must also be given to the mode by which the blood is kept continually 

 running its appointed course through the animal frame. This process, commonly called 

 CIRCULATION, takes place in the following manner, Man being an example : 



In the centre of the breast lies the heart, an organ composed of four chambers, the 

 two upper being termed auricles, and the two lower being distinguished by the title of 

 ventricles. These are only conventional terms, and do not express the office of the parts. 

 The auricles are comparatively slight in structure, but the ventricles are extremely 

 powerful, and contract with great force, by means of a curiously spiral arrangement 

 of the muscular fibres. These latter chambers are used for the purpose of pro- 

 pelling the blood through the body, while the auricles serve to receive the blood from 

 the vessels, and to throw it into the ventricles when they are ready for it. 



By the systematic expansion and contraction of the heart-chambers, the blood is sent 

 on its mission to all parts of the body, through vessels named arteries, gradually 

 diminishing in diameter as they send forth their branches, until they terminate in 

 branchlets scarcely so large as hairs, and which are therefore called " capillaries," from 

 the Latin word capillus, a hair. The formation of the capillary system is well shown 



CAPILLARIES IN SKIN OF 

 HUMAN FINGER. 



f.- 



CAPILLARIES OF HUMAN 

 TONGUE. 



CAPILLARY. 



by the accompanying sketches. The first figure exhibits a portion of capillaries which 

 are found in the fatty tissues, while the second and third are examples of the corre- 

 sponding vessels in the finger and the tongue. 



In the capillaries the blood corpuscules would end their course, were they not met 

 and welcomed by a second set of capillaries. These vessels take up the wearied and 

 weakened globules, carrying them off to the right-hand chambers of the heart, whence 

 they are impelled through a vessel known by the name of the " pulmonary artery," to 

 be refreshed by the air which is supplied to them in the beautiful structure known as 

 the lungs. Meeting there with new vitality if it may so be called the blood cor- 

 puscules throw off some of their effete portions, and so, brightened and strengthened, 

 are again sent through the arteries from the heart to run their round of existence, and 

 again to be returned to the heart through the veins. 



It is indeed a marvellous system, this constant circular movement, that seems to be 

 inherent in the universe at large, as well as in the minute forms that inhabit a single 

 orb. The planets roll through their appointed courses in the macrocosmal universe, as 

 the blood globules through the veins of the microcosm, man : each has its individual 



