THE FORMATION AND CIRCULATION OF LYMPH IN THE FROG

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Abstract
I. In 33 urethanized and 30 curarized frogs and 4 in which the lymph hearts were cauterized lymph was collected and fluid shown to be lost from the blood at a rapid but variable rate, according to the circulatory condition of the frog. During edema caused by stoppage of the lymph hearts induced by curarization in 6 frogs gains in weight of 16-28% were made in 6 hrs.; in 6 frogs in which urethane was added to the curare the increase was 10-32%, the urethane not having the expected effect of increasing the lymph flow. Fluid injected into the circulation did not remain long in the blood vessels. In 6 frogs 1 gastrocnemius was removed from each and weighed, the frog intravenously injected with 10 cc. Ringer''s solution, and later the other gastrocnemius removed and weighed. In each case the 2nd gastrocnemius had gained slightly in weight. The muscles being thus shown not to be the chief depot for water, comparative weighing experiments were made on all organs of 22 injected and 62 uninjected frogs; the skin was found to be the only tissue absorbing any amount of fluid. Hence it was inferred that the skin vessels were more permeable to fluid than other vessels.[long dash]II. A new method is here described for determining blood volume in the frog. This method is a micromodification of the dye injection method, and does not require the immediate sacrifice of the animal. The values obtained by this method are higher than those reported by earlier observers. The average blood volume is 8.74% of the body weight. A method is described for the direct observation of blood pressure in the anterior tibial artery of the frog. Initial values for blood pressure varied in 9 cases from 14.8 to 42.0 cm. of water. When blood pressure is watched for several hrs. it is maintained in quiescent frogs at practically the initial level. Exercise causes an immediate rise in blood pressure, with a rapid readjustment to the former level, due to transudation of fluid. Blood volume and pressure are mutually dependent and intimately related to the formation of lymph. Increase in blood pressure brought on by activity concentrates the blood, forcing more fluid out of the capillaries, and so increasing the flow of lymph. Quick return of lymph to the blood is provided for by the lymph hearts. [long dash]III. Capillaries of the frog''s skin are normally permeable to protein, but this substance, once it has left the capillaries, does not return through their walls, but takes the lymphatic route, passing through the lymph sacs, and eventually being returned to the blood by the lymph hearts. Experimental proof is offered as follows: (1) Lymph normally contains fibrinogen, albumins and globulins, the proteins of the plasma. (2) The plasma proteins may be almost entirely washed out of the blood by injecting large amounts of Ringer''s solution into the circulation of curarized frogs. The lymph hearts are stopped by the curare, and the lymph is drained off through cannulas inserted under the skin. The percentage of protein in the lymph risea quickly, then falls slowly as the blood is depleted. At the end of the experiment both blood plasma and lymph are vary low in protein. Foreign proteins injected into the circulation pass through the skin capillaries and may be recovered in the lymph. Hemoglobin and hemocyanin pass through with relative ease, while egg albumin and gelatin will pass through only after the capillaries have been rendered abnormally permeable by injection of Ringer''s solution. The latter is also true of colloidal carbohydrates. The integrity of the lymphatic system is essential to the frog, because of its important circulatory function in returning protein to the blood.

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