PHYSIOLOUICAI, STUDIES OF THE CHINOOK SALMON. 



441 



1 1 1 1 1 1 1 1 1 1 1 1 1 1 



the time between the cutting of the artery and the insertion of the cannula was thus 



reduced to a minimum. The cannula itself usually compressed the vein in the haemal 



arch enough to prevent bleeding, and the bleeding from the small cutaneous vessels, 



which may be considerable if left alone, was easily checked by a tight ligature 



thrown around the body just in front of 



the cut. This ligature should be laid f^^wv^^^ 



during the preliminary preparations. 



The blood pressure from the dorsal 

 aorta is quite strong in the salmon, 

 reaching as much as 58 millimeters of 

 mercury in the maximal pressure meas- 

 ured (fig. 4). The average pressure for 

 the six examples reported in Table VII is .">:->.:-> millimeters of mercury, with the 

 extremes of 14 and 58. The mean heart rate of this scries is 49.2 per minute, while 

 the average noted in connection with the measurements of ventral aortic pressure is 

 61 (for males alone 60). This lower average heart rate suggests the inference that 

 the resulting mean blood pressure is below the normal average. This is no doubt 

 possible on account of the slight loss of blood attendant on the operation, a loss 

 which, though small, is felt all the more on account of the relatively small amount 

 of blood in the salmon. 



KiG. 4.— Experiment Aug 28, 1902, No. 220, male; length, 490 

 millimeters. Blood pressure from the dorsal aorta. The 



strong pulse beat is noteworthy. HI 1 pressure, 57 milli- 



meters « >f mercury; heart rate, 48 per minute. 



Table VII. — Blood pressure and heart rate measured from the dorsal aorta. 



The striking thine- about the results of these measurements, notwithstanding 

 the criticism offered above, is the fact that the pressure in the caudal portion of the 

 dorsal aorta approaches so nearly that of the ventral aorta. It would seem that the 

 resistance to the blood flow through the gills is comparatively slight, and the reduction 

 of blood pressure correspondingly insignificant. This fact is further borne out b^y 

 the presence of the dorsal aortic pulse, which is generally strong and of considerable 

 amplitude. It would be of comparative interest if the pressure could be taken from 

 one of the efferent branchial arteries, but in the salmon this would be extremely 

 difficult, if not wholly impossible. The visceral branches of the aortic trunk are so 

 much atrophied in salmon from the spawning beds that the method of measurement 

 from these vessels, though very easy in the Selachii, is quite impracticable in the 

 salmon. 



