44>2 BULLETIN OF THE BUREAU OF FISHERIES. 



No synchronous measurements of the pressure in the ventral and in the dorsal 

 aortse have been made, on account of lack of duplicate, apparatus while in the field. 

 Consecutive measurements arc of little comparative value, owing- to the necessary loss 

 of blood in making- the transfer of the cannula from one vessel to the other in the 

 methods it was necessary to use. In the consecutive experiments reported it will lie 

 seen that the measurements taken second are considerably below the average, except 

 in a single experiment, No. 221. 



THE KATE AND FORCE OF THE HEART BEAT IN THE SALMON. 



The tracings of the blood pressure taken from the ventral aorta at a point so 

 near the heart, as was the case in the experiments reported in this paper, give 

 considerable information about the heart itself. The 26 specimens given in Table 

 III, page 437, give an average heart rate of 58.9 — in round numbers 60 — contractions 

 per minute, or 1 per second. This rate seems rather rapid for so large a fish. A 

 glance at the series of experiments shows a wide range of rates in different specimens, 

 the extremes being 34 and 86 per minute, respectively. There seems no close corre- 

 spondence between rate of heart beat and blood pressure. The three specimens 

 giving the highest ventral aortic pressures, Nos. 52, 54, and 61, with pressures of 



ItoWlWftv*/^^ 



■ 1 ■ ■ I ■ . ■ ■ I . 



FIG. 5. — Experiment Aug. 23, 1902, No. 212. female; length, 777 millimeters. Showing the maximal blood pressure in the 

 ventral aorta when that vessel is completely occluded. Pressure before occlusion of the aorta, 46 millimeters of mer- 

 cury; after occlusion, 113 millimeters. 



100, 120, and 108 millimeters of mercury, have heart rates of 57, 60, and 34 contrac- 

 tions per minute, respectively. It will be noticed, however, that the pulse pressure 

 of No. 61 is very high, a fact which accounts for the maintenance of a strong blood 

 pressure with a low heart rate. On the other hand, No. 23, which has a heart rate 

 of 86 per minute, has a blood pressure in the ventral aorta of only 47 millimeters, 

 while the average pressure of fish of this size is 60 millimeters. 



The pulse pressure, i. e., the increase of blood pressure accompanying each 

 discharge of the heart into the aorta, varies exceedingly. In general the slower the 

 rate the greater the amplitude of the pulse, though the exceptions are too numerous 

 to conclude that the pulse pressure is an index of the rate; neither is it an index of 

 the absolute pressure. Selected experiments indicate that there are factors to be 

 determined which correlate the force and rate of the heart beat against the resistance 

 to the discharge through the gills. 



The possible force of the heart is indicated by the experiment of compressing 

 the aorta, thus blocking the discharge of the blood and compelling the heart to con- 

 tract to its fullest capacity. The maximal pressure is surprisingly great in these 

 tests, as can lie seen by reference to Table VIII. 



