Observations and experiments on the mode in which various poisonous agents act on the animal body / by James Blake.

  • Blake, James, 1814-1893.
Date:
[1840]
Catalogue details

Licence: Public Domain Mark

Credit: Observations and experiments on the mode in which various poisonous agents act on the animal body / by James Blake. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    the instant they take place, by the use of the hemadynamometer, an instrument which indicates, by means of a column of mercury, the pressure sustained by the parietes of the blood-vessels, and which immediately becomes modified on any change being pro- duced, either in the action of the heart, or in the capillary circu- lation. (Exp. 2.) The following experiment furnishes an example of the time required for a substance to pass from the jugular vein to the capillaries of the pulmonary artery. It had been ascertained that soda and its salts possess the property of arresting the capil- lary circulation in the lungs. When this effect is produced, no more blood is sent into the left side of the heart and arterial system, and it follows, that the pressure sustained by the parietes of the arteries must be instantly diminished. Fifteen grains of soda dissolved in six drachms of water were injected into the jugular vein of a dog. Six seconds after the first portion of the injection was introduced, the pressure in the arterial system began to dimi- nish, and the mercury in the hemadynamometer speedily sank to zero, although the pulsations of the heart still continued.* (Exp. 3.) An experiment the reverse of the former was per- formed by connecting the hemadynamometer with the venous sys- tem. When the passage of the blood through the lungs is arrest- ed, it is evident that the venous system must become congested, and thus the pressure supported by the parietes of these vessels will be increased. In this instance six seconds elapsed between the introduction of the substance into the veins, and any percep- tible increase in the pressure. It would appear from these experiments that soda when intro- duced into the jugular vein affects the capillaries in the lungs in from four to six seconds; a space of time rather greater than that required by ammonia to traverse this distance. This might arise from two causes ; either that the diffusive power of some sub- stances is much greater than that of others, and that they thus may be transmitted from one part of the column of blood to another, independently of its progressive motion ; or that in some animals the circulation is going on much more rapidly than in others. The public.—Since the above was written, the experiments in question have been pub- lished in a memoir read at the Institute of France. * The time at which marked effects are produced might not be the moment at which the substance is applied to the tissue affected ; a slight interval probably elapses between the arrest of the capillary circulation in the lungs and the diminish- ed pressure in the arterial system. The time, therefore, in which these effects were observed is probably a second or two later than that on which the soda reached the capillaries. The importance of taking into eonsideration even these apparently trifling circumstances will be acknowledged, when it is shown that an interval of two or three seconds forms a considerable fraction of the whole of the time required for the circulation to be completed in.