Abstract
Methods for determining the blood volume of small animals are available, but all have one of two objections: (1) they require so much blood as to affect the subsequent blood volume of the animal, or may even cause its death; (2) they require the laborious preparation of standards consisting of dye-containing serum in uniform capillary tubes. Such standards are then presumed to be permanent.
Our method requires but 50 cmm. of blood, and the standard can be set up for each period of work in a few minutes. Moreover, the blood volume is determined directly, and not calculated from the serum volume by means of the hematocrit reading.
Adult albino rats have been used. Three mg. of nembutal per 100 gm. of body weight are injected intraperitoneally. As soon as the animal is sufficiently quiet, the jugular vein is exposed at the base of the neck by an incision parallel to its course. Then 0.3 cc. of 5% vital red is injected into the dilated bulb. The manner of injection is important. A one cc. tuberculin syringe fitted with a fine hypodermic needle is used. Exactly 0.3 cc. of the dye is drawn into the syringe, reading the mark against a strong light. The needle, pointing toward the rat's head, is introduced into the upper border of the pectoral muscle, grazes the upper edge of the clavicle and enters the vein through the muscle. The point is carried onward until it is visible in the jugular bulb. It is moved up and down to be sure it has not picked up the vein wall, after which the dye is injected under inspection. We wait 20 to 25 seconds while the vein clears of dye.
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