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Updated: June 21, 2025
*Blood Pressure and Velocity.*—The blood, in obedience to physical laws, passes continuously through the blood vessels, moving always from a place of greater to one of less pressure. Through the contraction of the ventricles, a relatively high pressure is maintained in the arteries nearest the heart.
The arguments in favor of the three ventricles of the brain have been, that those ventricles are the recipients of the animal spirits and of all the lymphs of the brain: the arguments in favor of the corpora striata have been, that these bodies constitute the marrow, through which the nerves are emitted, and by which each brain is continued into the spine; and from the spine and the marrow there is an emanation of fibres serving for the contexture of the whole body: the arguments in favor of the medullary substance of each brain have been, that this substance is a collection and congeries of all the fibres, which are the rudiments or beginnings of the whole man: the arguments in favor of the cortical substance have been, that in that substance are contained the prime and ultimate ends, and consequently the principles of all the fibres, and thereby of all the senses and motions: the arguments in favor of the dura mater have been, that it is the common covering of each brain, and hence by some kind of continuous principle extends itself over the heart and the viscera of the body.
Now this inner coat is wanting in the veins, whose walls sink in together when a cut is made in them, so that it is much easier to stop the flow of the blood in them. Furthermore, the veins are furnished inside at intervals with little doors, similar to those we noticed at the entrance of the auricles and ventricles of the heart.
The stimulus must regularly begin in the auricle, must be perfectly transmitted through the bundle of His to the ventricles, the ventricles must normally contract with the normal and regular force, the valves must close normally and at the proper time, the blood pressure in the aorta must be normally constant to insure the perfect transmission of the blood to the peripheral arteries and to insure the normal circulation through the coronary arteries, and the arterioles must be normally elastic.
Harvey's investigations led him to doubt also the accepted theory that there was a porosity in the septum of tissue that divides the two ventricles of the heart. It seemed unreasonable to suppose that a thick fluid like the blood could find its way through pores so small that they could not be demonstrated by any means devised by man.
On account of their important function in this operation the false vocal cords are called the 'breath-bands. Closure of the glottis by the inflation of the ventricles imposes no strain on the vocal cords. The theory of breath-control by "opposed muscular action" takes no cognizance of this operation. "Control of the breath in singing is effected by this automatic valvular action.
You will observe that there is a portion of each heart which is what is called the ventricle. Now the ancients applied the term 'heart' simply and solely to the ventricles.
All this is found the same in reptiles: except that the partition, which separates our two ventricles from each other, does not exist in them; and the heart has only one common room, in which, therefore, arterial and venous blood become mixed together.
Heart of a human embryo, six weeks old, front view. r right ventricle, t left ventricle, s furrow between ventricles, ta arterial bulb, af furrow on its surface; to right and left are the two large auricles.
Certain cases of hæmorrhage into the lateral ventricles of the brain also simulate tetanus, but an analysis of the symptoms will prevent errors in diagnosis. Cerebro-spinal meningitis and basal meningitis present certain superficial resemblances to tetanus, but there is no trismus, and the spasms chiefly affect the muscles of the neck and back.
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