. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 12 B. R. LUTZ AND L. C. WYMAX measurements), and it was noted that fluid would not enter the ventral aorta from the burette below 25 cm. urea-saline ( mrn. Hg\ A sudden increase of pressure averaging mm. Hg above the average -i"lic pressure existing in the dorsal aorta was found to constitute an adequate stimulus for cardiac inhibition (Fig. 2, B), and in one instance a difference as low as 3 mm. Hg produced the response (Fig. 2, C). Although urea-saline is considered to be a physiological solution, a control e
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 12 B. R. LUTZ AND L. C. WYMAX measurements), and it was noted that fluid would not enter the ventral aorta from the burette below 25 cm. urea-saline ( mrn. Hg\ A sudden increase of pressure averaging mm. Hg above the average -i"lic pressure existing in the dorsal aorta was found to constitute an adequate stimulus for cardiac inhibition (Fig. 2, B), and in one instance a difference as low as 3 mm. Hg produced the response (Fig. 2, C). Although urea-saline is considered to be a physiological solution, a control experiment was performed using heparinized fresh dogfish blood in the burette and its connections. A similar inhibitory response to increased pressure in the gill vessels was obtained (Fig. 1, B).. I;u;. 2. recorded by Hg manometer. Figures at left show pressure levels in mm. 11^. A. Simultaneous records of ventral (upper) and dorsal (lower) . ">rtic blood pressure. H. Ventral aortic blood pressure record. Threshold increase of pressure in tlie first branches of the \cntral aorta at T (33 cm. urea-saline, nun. I Ig). C. Same, threshold 25 cm. urea-saline ( mm. 1 Ig). D. Ventral aortic blood pressure record. Spontaneous ejection reflexes at R. Cardiac inhibition was obtained when the burette was opened and immediately closed, allowing only cc. of fluid to enter. Further- more, holding the burette open, until 5 cc. of fluid had entered the ventral aorta, did not increase or continue the initial inhibition during the period of flow. It follows that the effective stimulus is the initial increase of pressure per se, and not flow of fluid through the gill vessels. This was substantiated by blocking the flow through the gill capillaries so that the application of pressure alone served to stimulate. At- tempts to do this by tying the efferent branchial supply from the hemibranch and first holobranch were unsuccessful because of the numerous anastomoses
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
