Hand-book of physiology / by W. Morrant Baker and Vincent Dormer Harris.

  • William Morrant Baker
Date:
1892
Catalogue details

Licence: Public Domain Mark

Credit: Hand-book of physiology / by W. Morrant Baker and Vincent Dormer Harris. Source: Wellcome Collection.

Provider: This material has been provided by the Francis A. Countway Library of Medicine, through the Medical Heritage Library. The original may be consulted at the Francis A. Countway Library of Medicine, Harvard Medical School.

    149/914 (page 127)
    CH.v.] QUANTITY OF THE BLOOD. 12/ through the muscles, nerve centres, and glands, but is somewhat cooled on traversing the capillaries of the skin. Recently drawn blood has a distinct odour, which in many cases is characteristic of the animal from which it has been taken. It may be further developed also by adding to blood a mixture of equal parts of sulphuric acid and water. Quantity of the Blood.—The quantity of blood in any animal under normal conditions bears a fairly constant relation to the body-weight. The methods employed for estimating it are not so simple as might at first sight have been thought. For example, it would not be possible to get any accurate information on the point from the amount obtained by rapidly bleeding an animal to death, for then an indefinite quantity would remain in the vessels, as well as in the tissues; nor, on the other hand, would it be possible to obtain a correct estimate by less rapid bleeding, as, since life would be more prolonged, time would be allowed for the passage into the blood of lymph from the lym- phatic vessels and from the tissues. In the former case, therefore, we should under-estimate, and in the latter over-estimate the total amount of the blood. Of the several methods which have been employed, the most accurate appears to be the following. A small quantity of blood is taken from an animal by venesection ; it is defibrinated and measured, and used to make standard solutions of blood. The animal is- then rapidly bled to death, and the blood which escapes is collected. The blood-vessels are next washed out with saline solution until the washings are no longer coloured, and these are added to the previously withdrawn blood ; lastly the whole animal is finely minced with saline, solution. The fluid obtained from the mincings is carefully filtered, and added to the diluted blood previously obtained, and the whole is measured. The next step in the process is the comparison of the colour of the diluted blood with that of standard solutions of blood and water of a known strength, until it is discovered to what standard solution the diluted blood corresponds. As the amount of blood in the corre- sponding standard solution is known, as well as the total quantity of diluted blood obtained from the animal, it is easy to calculate the absolute amount of blood which the latter contained, and to this is added the small amount which was withdrawn to make the standard solutions. This gives the total amount of blood which the animal contained. It is contrasted with the weight of the animal, previously known. The result of many experiments shows that the quantity of blood in various animals averages -^ to T2T of the total body-weight.