Abstract
Results of previous workers from Starling 1 to Krogh and Nakazawa 2 have shown the colloid osmotic pressure of the blood serum to vary between 265-420 mm. of water pressure, with average values of approximately 310-360 mm.
Osmotic pressures reported here have been obtained with a greatly modified apparatus using aseptic technique, an accurately controlled constant temperature water bath at 30°C., and modified Ringers as a dialyzing agent. The figure shows osmometer tube (C) with (Dupont No. 300 plain transparent cellophane) membrane attached, which is filled with blood serum; (D) is capillary tube attachment for noting blood serum meniscus; (E) is stopcock to prevent rise of serum in capillary during development of pressure. (A) is fitted into (B) which shows saline tube (F) with side arm (G) for filling or for removing bubbles from serum tube through orifice (H) or side arm can be turned to groove (I) allowing air to enter outer system, thus preventing the production of a vacuum. The 3 parts are fastened together by means of springs over small glass hooks. The osmometer is immersed in a constant temperature bath up to the stopcock and attached to a manometer.
It has been inferred that a low serum protein value means a lowered serum osmotic pressure. Accordingly, a short series of readings was done on dog serum obtained from dogs which were undergoing plasma-pheresis 3 and whose serum protein values were consequently much lower than those of normal dogs, being from 3.65 to 5.27 gm. per 100 cc. of serum as compared with 6.35 to 6.60 gm. per 100 cc. of serum for the normal animals. The serum osmotic pressures (measured by Krogh's method 4 ), when compared with similar determinations on normal dogs, were also found to be definitely lower, 93 to 225 mm.
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