A textbook of human physiology / translated from [the] 6th German edition by W. Stirling.

Landois, Leonard

Date:: 1888

Credit: A textbook of human physiology / translated from [the] 6th German edition by W. Stirling. Source: Wellcome Collection.

Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.

189/980 page 137

$inuch as the heart. As the whole of the work of the heart is consumed in over- coming the resistance within the circulation, or rather is converted into heat, the body must be partly warmed thereby—(425-5 gramme-metres are equal to 1 heat-unit, i.e., the force required to raise 425*5 grarnmes to the height of 1 metre may be made to raise the temperature of 1 cubic centimetre of water V C). So that 204,000 heat-units are obtained from the transformation of the kinetic energy of the heart. One gramme of coal when burned yields 8080 heat-units, so that the heart yields as much energy for heating the body as if about 25 grammes of coal were burned within it to jjroduce heat. 94. BLOOD-CURRENT IN THE SMALLER VESSELS.—Methods. — The jnost important observations for this purpose are made by means of the microscope on transparent parts of living animals. Malpighi was the first to observe the cir- ■culation in this way in the lung of a frog (1661). The following parts have been employed :—The tails of tadpoles and small fishes; the web, tongue, mesentery, and Inngs of eiirarised iVogs ; the wing of the bat ; the third eyelid of the pigeon or fowl; the mesentery ; the vessels of the liver of frogs and newts, pia mater of rabbits, the skin on the belly of the frog, the mucons membrane of the inner surface of the human lip {Hiiter's Cheilangioscope, 1879); the conjunctiva of the eyeball and eyelids. All these may be examined by reflected light. [Holmgren's Method —In studying the circulation in the frog's lung, it must be inflated. A cannula with a bulge on its free end is placed in the larynx, while to the other end is fixed a piece of caoutchouc tubing. The lung is inflated and then the caoutchouc tube is closed, after which the lung is placed iu a chamber with glass above and below, a)id examined microscopic- ally.] [Entoptical appearances of the circulation (Furkinje, 1815). Under certain conditions a person may detect the movement of the blood-corpuscles within the blood-vessels of his own eye. The best method is that of Rood, viz., to look at the sky through a dark blue glass, or through several pieces of cobalt glass placed over each other {Helmholfz).] Form and Arrangement of Capillaries.—Regarding the form and arrangement of the capil- laries, we find that— 1. The diameter which, in the finest, jjcrmits only the passage of single corpuscles in a row— •one behind the otlier—may vary from 5 yn to>2 (jl, so that 2 or more corpuscles maj'^ move abreast when the capillary is at its widest. 2. The Zc/i(^/A is about 0 5 mm. They terminate in small veins. •3. The nicmbcr is very variable, and the capillaries are most numerous in those tissues where the metabolism is most active, as in lungs, liver, muscles—less numerous in the sclerotic and iu the nerve-trunks. 4. They form numerous anastomoftes, and give rise to networks, whose form and arrangement ure largely determined by the arrangement of the tissut; elements themselves. They form simple loops in the skin, and polygoiuil networks in the serous membranes, and on the surface of many gland tubes ; they occur in the form of elongated networks, with short connecting branches in muscle and nerve, as well as between the straight tubules of the kidney ; they con- verge radially towards a central point in the lobules of the liver, and form urrhen in the free margins of the iris, and on the limit of the sclerotic and cornea. [Direct Termination of Arteries in Veins.—Arteries sometimes bMininate din^ctly in veins, without the intervention of capillaries, e.g., in the ear of the rabbit, iu the tci niinal phalanges of the fingers and toes in man and some animals, in the cavernous tissue of the penis. They may be regarded as secondary channels which protect the circulation of adjacent parts, and they may also be related to the heat-regulating mechanisms of peripheral parts {Hoyer).] In connection with Ihe termination of arteries in capillaries, it is imjuirtant to nsccrtain if the arterioles are terminal arteries, i.e., if they do not form any further anastomoses with other similar arterioles, but terminate directly in capillaries, and thus only communicate by capillaries with neighbouring arterioles—or the arteries may anastomose with other arteries just before they break up into capillaries. This distinction is important in connection with the nutrition of parts supplied by such arteries {Cohnhcim). Capillary Circulation.—On observing the capillary circulation, we notice that the red corpuscles move only in the axis of the current (axial current), while the lateral transparent plasma-current flowing on each side of this central thread is free from these corpuscles. [The axial current is the more rapid.] This plasma layer or Poiseuille's space is seen in the smallest arteries and veins, where f are$

A textbook of human physiology / translated from [the] 6th German edition by W. Stirling.

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