438 



BULLETIN OF THE BUREAU OF FISHERIES. 



Table IV. — Showing the range of variations in tin veiitxil aortic Mood protean' in normal salmon from the 



spawning beds. 



It must be remembered, however, that in a series of experiments of this nature 

 the artificial conditions tend to lower the natural or normal pressure which exists 

 while the fish is in its natural habitat. Such events as loss of blood, inadequate 

 respiratory arrangements, change in external pressure on the surface of the body 

 exerted by the air as compared with that of the water, increase of body temperature in 

 the air over that in the water out of which .the specimen has just been taken, as well 

 as the general indeterminate conditions that affect the vitality of these river salmon — 

 all these act to minimize the observed pressures. 



Fi*i. 3. — Experiment Aug 23, 1902, No. 210, female: length, 672 millimeters. Blood pressure from the ventral aorta, show- 

 ing the rhythmic interference of the respiratory movements with the pulse pressure. 



The 11 males used, varying from 428 to 935 millimeters in length, gave an average 

 ventral aortic pressure of 74.3 millimeters of mercury. This is the equivalent of 101 

 centimeters of water. With the fishes, as with the higher animals, the larger speci- 

 mens of otherwise equal physical condition may be expected to give slightly higher 

 pressures. Indeed, a reference to Table V below will show at a glance that such is 

 the case for the salmon. The mean or average pressure for all the specimens 

 between 70 and 100 centimeters in length is 82.6 millimeters of mercury, the equiva- 

 lent of 112.4 centimeters of water pressure. The pressure in the smaller specimens 

 between 40 and 70 centimeters in length is only 61 millimeters of mercury or 83 

 centimeters of water. The relatively slight intrinsic value of the smaller tish, which 

 are invariably males, and the greater facility in securing and manipulating them in 

 experiments, leads to their use in larger numbers. When the mean pressure is com- 

 pared in the males alone, the difference is much more striking. The 7 males between 

 40 and 70 centimeters in length gave an average pressure of 60 millimeters, while 

 the 5 larger males between 70 and 100 centimeters long averaged 96 millimeters 

 pressure. The pressure of 74.3 millimeters of mercury may. therefore, be considered 

 somewhat lower than the average pressure of prime male salmon. 



