32 KANSAS UNIVERSITY SCIENCE BULLETIN. 



of a definite volume, velocity, and temperature entered the 

 mouth through a forked glass tube covered with rubber tubing. 



As soon as the water enters the mouth and flows out of the 

 gill slits over the body, thus keeping the skate practically sub- 

 merged, and the netting comes in contact with the body, the 

 fish is perfectly quiet and remains so for hours, apparently 

 contented and comfortable. A cannula, filled with 20 per cent 

 glucose or glucose and 1 per cent ammonium oxalate, is in- 

 serted in one of the side branches of the aorta and joined to a 

 delicate mercury manometer placed quite on a level with the 

 blood vessels. To the open end of the manometer is attached 

 a Hurthle manometer, which records the heart action, while 

 the pressure is read off directly from the manometer. • 



By means of a silk loop one of the gill arches is attached to a 

 light lever which records the respiratory movements. In con- 

 trol experiments the tip of the ventricle was exposed and by 

 means of a silk loop joined to a light lever, so that in addition 

 to the above records, separate ones were obtained of the rate 

 and force of the heart's activity. 



The salts employed in the experiments were all chemically 

 pure, either from Kahlbaum or specially prepared in the lab- 

 oratory, and they were all standardized. The water employed 

 in making up the solutions was twice distilled in glass. 



To avoid mechanical stimulation a cannula, to which was 

 connected a rubber tube, was inserted either in the median or 

 lateral caudal vein and tied in place. Subsequently 4 cc. of the 

 solution per kilo weight of fish was slowly pressed from a 

 graduated glass tube into the cannula by means of a rubber 

 bulb attached to its upper end. 



During the inspiratory phase the mouth and spiracles are 

 opened, the floor of the mouth is lowered, the gill clefts or ex- 

 ternal branchial apertures are closed, and water enters the 

 mouth and spiracles. In the expiratory phase the mouth and 

 spiracles close, the floor of the mouth returns to its normal 

 position or is elevated and the gill clefts open to allow the 

 water to escape. Occasionally a peculiar spouting takes place 

 during which water is thrown from the mouth and spiracles. 

 This is observed in the aquarium also and may be due to irri- 

 tation, touch, stimulation of the mucous lining of the mouth by 

 slime particles or vitiated water. 



I first investigated the effect of different concentrations of 



