Volume 1

A text-book of human physiology : including histology and microscopical anatomy with special reference to the requirements of practical medicine / by L. Landois ; translated from the seventh German edition with additions by William Stirling.

Landois, L. (Leonard), 1837-1902. Lehrbuch der Physiologie des Menschen. English

Date:: 1891

Credit: A text-book of human physiology : including histology and microscopical anatomy with special reference to the requirements of practical medicine / by L. Landois ; translated from the seventh German edition with additions by William Stirling. Source: Wellcome Collection.

146/602 page 106

$(3) If, however, fluid be pumped interruptedly or by jerks into sxn elastic tube filled with fluid, in which there is already a continuous current, the movement of the current is combined with'the wave movement. We must carefully distinguish the movement of the current of the fluid, i.e., the translation of a mass of fluid through the tube, from the wave-movement, the oscillatory movement, or movement of change of form in the column of fluid. In the former the particles are actually translated, while in the latter they merely vibrate. The current in elastic tubes is slower than the wave-movement, which is propagated with great rapidity, ihis last case obtains in the arterial system. The blood in the arteries is already in a state of con- tinual movement, directed from the aorta to the capillaries ; by means of the systole of the left ventricle a quantity of fluid is suddenly pumped into the aorta, and causes a. positive wave,\hQ pulse-wave which is propagated with great rapidity to the terminations of the arteries, while the current of the blood itself moves much more slowly. Rigid and Elastic Tubes.—If a quantity of fluid be forced into a rigid tube under a certain pressure, the same quantity of fluid will flow out at once at the other end of the tube, provided there be no special resistance. In an elastic tube, immediately after the forcing m of a quantity of fluid at first only a small quantity flows out, and the remainder flows out only after the propelling force has ceased to act. If an equal quantity of fluid be periodicaUy injected into a rigid tube, with each jerk an equal quantity is forced out at the other end of the tube, and the outflow lasts exactly as long as the jerk or the contraction, and the pause between two periods of outflow is exactly the same as between the two jerks or contractions. In aii elastic tube it is difl'erent, as the outflow continues for a time after the jerk; hence it follows that a continuous outflow current will be produced in elastic tubes, when the time between two jerks is made shorter than the duration of the outflow after the jerk has been completed. When fluid is pumped periodically into rigid tubes, it causes a sharp abrupt out- flow synchronous with the inflow, and the outflow becomes continuous only when the inflow is continuous and uninterrupted. In elastic tubes, an intermittent current under the above conditions causes a continuous outflow, which is increased with the systole or contraction. 65. STEUCTURE AND PROPERTIES OF THE BLOOD-VESSELS.—In the body the large vessels carry the blood to and from the various tissues and organs, while the thin-walled capillaries bring the blood into intimate relation with the tissues. Through the excessively thin walls of the capillaries the fluid part of the blood transudes, to nourish the tissues outside the capillaries, so that the capillary wall is permeable to fluids and gases, and, we shall see, also to the red and white corpuscles of the blood. [At the same time fluids pass from the tissues into the blood. Thus, there is an exchange between the blood and the fluids of the tissues. The fluid after it passes into the tissues consti- tutes the lymph, and acts like a ^ivQdim irrigat- ing the tissue elements.] 1. The arteries are distinguished from veins by their thicker walls, due to the greater develop- ment of smooth muscular and elastic tissues— the middle coat (tunica media) of the arteries is specially thick, while the outer coat (t. adventitia) is relatively thin. [When cut across, the walls do not collapse, as is the case with the thin-walled veins. The absence of valves is by no means a characteristic feature.] A typical artery consists of three coats (figs. 79, 80). (1) The tunica intima, or inner coat, consists of a layer of {a) irregular, long, fusiform, nucleated, squamous cells forming the excessively thin transparent endothelium im- mediately in contact with the blood-stream. [Like other endothelial cells, these cells are held together by a cement substance, which is blackened by the action of silver nitrate and subsequent exposure to hght.] Outside this hes a very thin, more or less fibrous, layer—sub-epithelial layer—in which numerous spindle or Fig. 79. Coats of a small artery, a, endothe- lium ; b, internal elastic lamina ; c, circular muscular fibres of the middle coat ; d, the outer coat.$