178 THE HUMAN HEART. 



more distinctly divided, and in the capillaries the red globules are in 

 the highest state of discrimination, fit for supplying from their bosoms 

 living nutriment and warmth, and whatever depends upon the most 

 individual endowments. In the great vessels the blood is in public, 

 exercising general offices, and thronging the body to keep it wide 

 and open ; in the capillaries it is at home, its freedom, power, and 

 fluidity raised to the greatest pitch, and subject to the still influences 

 of a higher spirit than its own. Accordingly the capillaries are 

 more plainly under the direction of the brain, than the larger 

 vessels j their exquisite nervous coats undergo greater proportional 

 changes in calibre, and enjoy more individuality in differents parts 

 than the Herculean aorta and its tubes ; the emotions of the nerves 

 being almost omnipotent in their influence over these kindred and 

 subtle disciples. For the most part the blood-globules march in 

 single file through the capillaries ; but under the influence of cold, 

 stimulants, or inflammation, the latter will either close, so as appa- 

 rently to admit no red particles, or will enlarge considerably enough 

 to give passage to several rows abreast. A familiar instance of the 

 power of the mind or nerves upon this system, is seen in the pheno- 

 menon of blushing, in which the modest emotions, giving all place 

 to the pressure about them, instantaneously relax an outspread field 

 of capillaries, which lose their straight-laced dignity, and red blood 

 is injected into vessels that before carried only colorless fluid, or in 

 which the amount of red blood is now so greatly increased as to glow 

 through the skin of the face and neck, and tinge them with apparent 

 crimson. If we generalize this common fact, we observe what a 

 prodigious sway the brain must exercise over these blood-vessels. 

 The capillary system is coextensive with the body, for looking from 

 the heart as a centre, the framework of every organ and part con- 

 sists of capillaries. These, the brain and nerves have the power of 

 expanding and constringing in any place, or any number of places, 

 in a moment ; of producing secretions or stopping secretions at will ; 

 of varying the life that comes from without to any particle of the 

 frame. In short, the circulation in its active and flexible part, is 

 held in the leashes of the brain, and the accommodation of the 

 blood system to the existing state of the body and mind depends 

 mainly on the nerves acting on the capillaries. Nay, the texture of 



