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BULLETIN OF THE BUREAU OF FISHERIES. 



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intervals as the heart tilled with blood, a phenomenon I have 

 noticed in quite a number of different species of tishes. 

 Figure 7 shows the effects of a series of short stimulations 

 of the vagus in a large specimen, 110 centimeters in length. 



No accelerator influences were noticed in any of the 

 experiments of this series, though I ought to say that the 

 work on the nervous coordination of the circulatory system 

 has not been completed. 



There is a well-defined respiratory influence on the cir- 

 culation in the salmon. This finds expression in the tracings 

 in a rhythmic variation in the pulse pressure and to a slight 

 extent in the total blood pressure in the ventral aorta. The 

 respiratory movements consist of alternate opening and 

 closing of the inferior maxilla and the opercles. The total 

 result of the movement is a rhj'thmical variation in the pres- 

 sure of the pericardial sac exerted through that part of the 

 wall formed by the branchial apparatus. This movement 

 has been described in other tishes (Leud&cus dobuld) as 

 exerting an aspiratory function which materially assists in 

 the return of blood to the heart." Be this as it may, it 

 seems clear from my experiments that the respiratory move- 

 ments exert an influence which increases the pulse pressure 

 when it falls together in time with the heart beat and 

 decreases the pulse pressure when in opposite phase. The 

 respiratory rate 1 is so nearly synchronous with the heart rate 

 that the resulting curve, illustrated by figure 3 (p. 438), often 

 presents a very marked similarity to the vibrations of a reed 

 or tuning fork showing beats. No respiratory influence 

 was noticed on the blood pressure in the dorsal aorta. 



SUMMARY. 



In a review of these experiments on the circulatory 

 apparatus, one can not but note the general vigor of the 

 heart and circulation in the salmon. The main facts may 

 be summarized as follows: 



1. The heart rate is relatively high, the force of the 

 beats as measured by the pulse pressure is strong. 



'2. The pressure in the ventral aorta is ample to main- 

 tain a good and efficient circulation even in old specimens 

 that are otherwise too weak to keep themselves from being 

 caught on the retaining racks. 



3. This ventral aortic pressure is diminished compara- 

 tively little by the branchial circulation, with the net result 

 that the dorsal aorta has a strong pressure to drive the blood 

 into the muscles, a fact of vital significance when viewed in 

 connection witli the migration journey of the salmon. 



« Brunnings, W., Zur Physiologie des Kreislaufes der Pische. Pfliiger'8 Archiv f. d. ges. Physiologie, 75, 1899, 599. 



