PHYSIOLOGICAL STUDIES OP THK CHINOOK SALMON. 433 



METHODS. 



The size of Oncorhynchus tschawytscha, individuals of which often weigh as 

 much as 40 and 50 pounds, makes this a fish difficult to handle, especially since it suc- 

 cumbs rather quickly to artificial conditions. To take a salmon out of the water in 

 which it lives and to keep it alive under conditions which will permit of physiologi- 

 cal measurements is indeed about as difficult as putting a mammal under the water 

 for such a purpose, and for much the same reasons. 1 have been able, however, to 

 keep salmon alive under fairly normal conditions for as much as twenty minutes — in 

 one case, forty-two minutes. The procedure was as follows: A salmon holder was 

 made of abroad board supplied at one end with a grooved block, which was fitted 

 over the nose. A similar block for the back was also used for the smaller fishes. A 

 narrow strip of sail canvas was tacked to one edge of the board from a point oppo- 

 site the shoulder-girdle to some distance back toward the tail. The head end of the 

 holder was cut out in such a way as to allow free movement of the operculum in 

 respiration. The salmon was placed on its side on this board, quickly wrapped in tin 1 

 canvas, and tied to the board by stout twine bands around the nose, the shoulder-girdle, 

 and at intervals along the body and around the tail. The gills were aerated by a stream 

 of water from a garden hose which siphoned water from the hatchery flume, the sur- 

 face of which was about .""> feet above the operating table. The hose was inserted into 

 the mouth and the water was allowed to flow freely out over the gills and escape on 

 the tables and floor. Especial care was taken to have both opercles freeand to direct 

 the stream of water so that it irrigated the gills freely on both sides. The lower jaw 

 was left free to make its respiratory movements, though these movements, of course, 

 did not affect the artificial respiration. Blood-pressure measurements and respira- 

 tory counts were the tests made upon the salmon under these conditions. 



Blood-pressure measurements were desired both of the ventral and dorsal aorta 1 . 

 The difficulties in the way of measuring the pressure in the ventral aorta proved 

 exceptionally great. The pericardial cavity extends forward and includes the tonus 

 arteriosus and the origin of the short ventral aorta. The aorta almost immediately 

 makes a sharp turn upward toward the base of the. branchial apparatus, where the 

 afferent branchial arteries have their origin. These branchial arteries pass at once to 

 the gillarches and it is impossible to isolate any one of them without injuring the 

 delicate gill structure. This difficulty, together with the great coagulability of the 

 blood, was sufficient to invalidate all the efforts to lead off the blood pressure from 

 these vessels. The ventral aorta itself, though deep-seated in these large fishes, is 

 more easily exposed, and after considerable practice 1 was able to make the necessary 

 dissection accurately and quickly. The pectoral arch which covers the pericardial 

 region is cartilaginous in the salmon. In exposing the ventral aorta it was necessary 

 to cut aw T ay the greater part of the muscles of the gular region, together with the 

 anterior portion of the pectoral arch down to the wall of the pericardium, and to slit 

 open the extreme anterior ventral portion of the pericardium. A slight loss of 

 blood attends this operation, but all delicate vessels are quickly and effectively 

 stopped by rapid blood-clotting. It is evident that one can not insert a cannula into 

 the ventral aorta in the usual way — i. e.. by ligation. The vessel is too easily torn 

 to permit the use or insertion of the form of cannula such as Fiek's, and the blood 



