VENOUS. 679 



action of elaboration is exerted on the absorbed fluid. Of this we have 

 the most convincing proof in certain experiments by M. Magendie. 1 In 

 exhibiting to his class the mode in which medicines act upon the sys- 

 tem, he showed, on a living animal, the effects of introducing a quantity 

 of water, of the temperature of 104 Fah., into the veins. In perform- 

 ing this experiment, it occurred to him to notice what would be the 

 effect produced by artificial plethora on the phenomena of absorption. 

 Having injected nearly a quart of water into the veins of a dog of middle 

 size, he placed in the cavity of the pleura a small dose of a substance 

 with the effects of which he was familiar, and was struck with the fact, 

 that they did not exhibit themselves for several minutes after the ordi- 

 nary period. He immediately repeated the experiment, and with a 

 like result. In several other experiments, the effects appeared at the 

 ordinary time, but were manifestly feebler than they ought to have 

 been from the dose of the substance employed ; and were kept up much 

 longer than usual. 



In another experiment, having introduced as much water as the ani- 

 mal could bear without perishing, which was about two quarts, the 

 effects did not occur at all. After having waited nearly half an hour 

 for their developement, which generally required only about two minutes, 

 he inferred, that if the distension of the bloodvessels was the cause of 

 the defect of absorption, if the distension were removed, absorption 

 ought to take place. He immediately bled the animal largely in the 

 jugular ; and, to his great satisfaction, found the effects manifesting 

 themselves as the blood flowed. He next tried whether, if the quantity 

 of blood were diminished at the commencement of the experiment, ab- 

 sorption would be more rapid ; and the result was as he anticipated. 

 An animal was bled to the extent of about half a pound ; and the effects, 

 which did not ordinarily occur until after the second minute, appeared 

 before the thirtieth second. As the results of these experiments seemed 

 to show, that absorption is in an inverse ratio to the degree of vascular 

 distension, he inferred, that it is effected physically ; is dependent upon 

 capillary attraction ; and ought to take place as well after death as 

 during life. To prove this, he instituted the following experiments. He 

 took a portion of the external jugular of a dog, about an inch long and 

 devoid of branches. Removing carefully the surrounding areolar tissue, 

 he attached to each extremity a glass tube, by means of which he kept up 

 a current of warm water within it. He then placed the vein in a slightly 

 acid liquor, and carefully collected the fluid of the current. During the 

 first few minutes, it exhibited no change ; but, in five or six minutes, 

 became sensibly acid. This experiment was repeated on veins taken 

 from the human subject with like results; and not only on veins but on 

 arteries. 



Similar experiments were next made on living animals. He took a 

 young dog, about six weeks old, whose vessels were thin, and, conse- 

 quently, better adapted for the success of the experiment, and exposed 

 one of its jugular veins. From this he dissected entirely the surround- 

 ing matter, and especially the areolar tissue, and the minute vessels 

 that ramified upon it ; and placed it upon a card, in order that there 



1 Op. citat., ii. 273. 



