Elements of human physiology / by L. Hermann ; translated from the sixth edition by Arthur Gamgee.

  • Gamgee Arthur, 1841-1909.
Date:
1878
Catalogue details

Licence: Public Domain Mark

Credit: Elements of human physiology / by L. Hermann ; translated from the sixth edition by Arthur Gamgee. Source: Wellcome Collection.

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

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    capillaries to the systemic, the blood is rich in oxygen, and conse- quently bright red or arterial; on the other hand, during its passage from the systemic to the pulmonic capillaries, it is poor in oxygen, but rich in carbonic acid, and therefore dark red or venous. The whole circulation, therefore, naturally divides itself into two halves, an arterial and a venous. At the commencement of each of the trunks of the vascular system (the one the arterial, the other the venous) is placed the principal motor apparatus, in the form of two contractile pouches, supplied with valves—the two halves of the heart—the left being on the arterial side of the circulation (commencement of the aorta), the right on the venous (commepcement of the pulmonary artery). Eeckoning from the heart forwards, all those vessels which carry blood to a capillary system are called arteries, whilst those carrying the blood from a capillary system are called veins. There are therefore two arterial and two venous systems. The systemic arterial system (the aortic system) carries arterial blood from the left side of the heart into the systemic capillaries; the systemic venous system carries this blood, now become venous, into the right side of the heart, from which the pulmonary arterial system carries the venous blood into the pulmonary capillaries, and the pulmonic venous system returns this blood, again become arterial, into the left side of the heart. Although the complete circulation forms one single circuit, the course of the blood from the left side of the heart through the sj-slemic capillaries to the right side of the heart is often erroneously described as the greater or systemic cii'- culation, the other as the lesser or pulmonary circulation. One portion of the systemic venous blood, viz. that coming from the capillaries of the intestines and spleen, unites to form one vein (the portal vein), which does not proceed directly to the right side of the heart, but branches out, like an artery, into a second capillary system in the liver, whence it passes into veins leading du-ect to the heart. This section of the vascular system is erroneously called the portal circulation. Since the sum of the diameters of the branches of an artery almost always exceeds the diameter of the trunk, the sum of the diameters of the vascular system must in general increase with its ramifications, and consequently is smallest in the two trunks (the aorta and pulmonary artery), and greatest in the capillaries. The vessels, especially the arteries, are very elastic. Amongst the motive powers producing the circulation of the blood the movements of the heart occupy the first place. The description of the circulation as a whole will therefore be preceded by an account of the most essential facts relating to the heart.