Manual of physiology / by William Senhouse Kirkes ; assisted by James Paget.

  • Kirkes, William Senhouse, 1823-1864.
Date:
1849
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Licence: Public Domain Mark

Credit: Manual of physiology / by William Senhouse Kirkes ; assisted by James Paget. Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

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    five seconds after injection. Still greater rapidity of transit has been observed by Mr. J. Blake (xciv. Oct., 1841), who found that nitrate of baryta injected i*nto the jugular vein of a horse could be detected in blood drawn from the carotid artery of the opposite side in from fifteen to twenty seconds after the injection. In six- teen seconds a solution of nitrate of potash, injected into the jugular vein of a horse, caused complete arrest of the heart's action, by entering and diffusing itself through the coronary arteries. In a dog, the poisonous effects of strychnia on the nervous system were manifested, in twelve seconds after injection into the jugular vein ; in a fowl, in six and a half seconds, and in a rabbit in four and a half seconds. In all these experiments, it is assumed that the substance in- jected moves with the blood, and at the same rate as it, and does not move from one part of the organs of circulation to another by diffusing itself through the blood or tissues more quickly than the blood moves. The assumption is so probable that it may be con- sidered nearly certain that the times above-mentioned, as occu- pied in the passage of the injected substances, are those in which, the portion of blood into which each was injected was carried from one part to another of the vascular system. It would, there- fore, appear that a portion of blood can traverse the entire course of the circulation, in the horse, in half a minute; of course it would require longer to traverse the vessels of the most distant part of the extremities than to go through those of the neck; but taking an average length of vessels to be traversed, and assuming, as we may, that the movement of blood in the human subject is not slower than in the horse, it may be concluded that one minute, which is the estimate usually adopted of the average time in which the blood completes its entire circuit in man, is rather above than below the actual rate. Another mode of estimating the general velocity of the circu- lating blood is by calculating it from the quantity of blood supposed to be contained in the body, and from the quantity which can pass through the heart in each of its actions. But the conclusions arrived at by this method are less satisfactory. For the estimates both of the total quantity of blood, and of the capacity of'tke'clVJ* • ties of the heart, are as yet only approximated to the truth, Still, the most recent and careful of the estimates thus made accord with those already mentioned : for Valentin has, frorr these data, calculated that the blood may all pass through thr heart in from 43| to 62-f seconds. The estimate from the speed at which the blood may be seer moving in transparent parts is not opposed to this. For, a< already stated (p. 109), though the movement-through the capil. laries maybe very slow, yet the length of capillary vessel througl