HYDE: EXPERIMENTS ON THE SKATE. 31 



its peculiar influence upon the life phenomena of respiration 

 and heart action and blood pressure. To which of these must 

 be ascribed the important changes produced in respiration and 

 cardiac activity and blood pressure is a question with which 7 

 shall not for the present concern myself, since in addition to 

 the experiments which I conducted it would be necessary, as 1 

 later saw, to carry on extensive physical and chemical investi 

 gations for which I lacked the time. I shall content myself, 

 therefore, by simply stating my method and observations, and 

 not attempt theoretical considerations of the underlying 

 causes, trusting that the data obtained from over 200 experi- 

 ments will aid in the correct interpretation of results secured 

 by other investigators working upon problems related to those 

 that I undertook. 



According to Garry- and Sumner^ the percentage of salts in 

 the skate and selachian's blood does not differ from that in 

 sea water. The lowering of the freezing point being — 1.8° C. 

 and the osmotic pressure twenty-two atmospheres, the sea 

 water is therefore isotonic with the skate's blood, while Bag- 

 lioni'^ estimated it isotonic with an m% NaCl or a 2 per cent 

 NaCl plus 2.5 per cent urea. Although the osmotic pressure 

 of the selachian's blood is the same as sea water, its salt con- 

 tent is less, but the lowering of the freezing point is compen- 

 sated by the urea in the blood. 



Employing Welcker's method, I ascertained that a small 

 skate weighing from 550 to 700 grams possessed 25 to 30 grams 

 of blood, or about one-twentieth of the body weight. Harris^ 

 states that the weight of the blood in the skate is only one- 

 fortieth of the body weight, but he does not describe the method 

 employed for ascertaining his data. 



Although there are wide variations in blood pressure, I 

 found that the mean pressure for an average-sized skate was 

 about 20 mm. of mercury. 



The photograph on plate X illustrates one of the methods 

 employed for securing records of the respiratory and cardiac 

 action and blood pressure. The skate was placed ventral side 

 up on an inclined board, partly submerged in water, and held 

 in place by fish netting; a constant stream of fresh sea water 



2. Garry, W. E. Biological Bulletin, 1905, vol. VIII, No. 4, p. 257. 



3. Sumner, F. B. Bulletin Bureau of Fisheries, 1906, p. 596. Baglioni. Zentralblatt 

 fiir Physiologic, 1905, vol. XIX, p. 12. Harris. D. F. Journal of PhysioloKy. 1903, 

 vol. XXX, Nor. 3 a^d 4, p. 319. 



