CHAPTER V. 



AXGIOLOGY. 



UNDER this beading we describe the organs of circulation, by the 

 action of which certain fluids are propelled through the body. 

 It is customary to divide this branch of the subject into two 

 sections, considering respectively the Blood-Vascular and Lym- 

 phatic Systems. 



BLOOD- VASCULAR SYSTEM. 



This involves the consideration of the Blood, a fluid which 

 supplies nutriment to the tissues, and receives effete material 

 from them ; the Heart, a muscular organ, which, by its contrac- 

 tion, initiates the motion of the blood ; the Arteries, a series of 

 tubes which convey the blood from the heart to all parts of the 

 body ; the Veins, tubes which return that fluid to the heart; 

 and the Capillaries, minute tubes joining the smaller arteries 

 and veins. 



BLOOD. 



Blood is a fluid tissue, which nourishes all living structures, 

 being the medium by which nutritive material is conveyed to, 

 and effete or waste material conveyed away from, the solid 

 tissues. It is an opaque, thickish, clammy fluid, with a peculiar 

 odour, sickly saline taste, and alkaline reaction. Its colour 

 varies in different parts of the same animal, that in the arteries 

 being bright red or scarlet, while the blood in the veins is of a 

 dark purplish hue. 



When examined microscopically, the blood is found to consist 

 of minute corpuscles, and a clear, transparent, yellow fluid, the 

 liquor sanguinis, or plasma, in which the corpuscles float. 

 The corpuscles are of two kinds, the red, and the white or 

 colourless ; the former, by far the more numerous, exist in vary- 



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