56 



ANNALS NEW YORK ACADEMY OF SCIENCES 



after ; 14, feeble, at fifty-five minutes ; 8, very feeble, at sixty-seven min- 

 utes; after which the experiment stopped. In some cases, the diminu- 

 tion in respiratory rate toward death was still more marked. Moreover, 

 the respiratory movements gradually became less forcible. Toward death, 

 they were very weak and consisted of but gentle movements of the gill 

 covers, to the eye ineffective as compared with normal respirations. The 

 respiratory movements at times ceased for a period altogether and then 

 suddenly broke forth with rapidity and force, soon fading, however, to 



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''^^■\f^\N^\rl'N^ 



..^W..^AAa,,B''^^^"^^'^V'^^'\.^ 



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7 8 



Fig. 10. — Shoicing changes in hlood pressure of Mustelus canis due to immersion in 



fresh water 



complete cessation. Eespiration ceases before the heart stops. Now and 

 then in normal respiration slightly convulsive movements of the gill ap- 

 paratus is observable. These have been noted by Hyde ('04-'08) in the 

 case of the skate. She drew the conclusion that these movements consti- 

 tute an attempt on the part of the fish to force a sudden strong current 

 of water through the gill apertures, the effect of which is to clean the gill 

 membranes of any foreign matter collected from the sea-water during the 

 course of normal respirations. After the fresh water was turned on, one 

 of the commonly observable effects consisted of violent respiratory spasms 

 accompanied by movements of the whole head. These spasms increased 



