(3 ANNALS NEW YORK ACADEMY OF SCIENCES 



the cartilaginous fishes are isotonic with the sea-water. It should be 

 noted here that the A of the sea-water at Naples^ where Bottazzi worked, 

 is much greater than that at Arcachon and Woods Hole, where Eodier 

 and Garrey respectively worked, and yet the blood of the elasmobranchs 

 from all three regions is approximately isotonic with the surrounding 

 medium. Bottazzi ('08) came to the conclusion that the urea, found in 

 such large quantity in the blood, is formed by the muscles. Baglioni 

 ('05) corroborated von Schroeder's '90 statement with regard to the urea 

 in selachian blood. He also found that the elasmobranch heart would 

 continue to beat if filled with a solution of equal parts of urea and 

 sodium chloride, to which a trace of calcium, salt was added. Dakin ('08) 

 found marked changes in the osmotic pressure and chlorine content of 

 the blood of the dog-fish when the animal was immersed in fresh water. 

 One of his general conclusions is that the limiting membranes of the body 

 are impermeable to salts and that the changes observed in the blood are 

 due to variations in the relative amount of water. The limiting mem- 

 branes of the body are semi-permeable. Hyde ('08) found that injection 

 of solutions of sodium, calcium, potassium and magnesium salts in differ- 

 ent degrees of dilution produced changes in the blood pressure and the 

 respiratory and cardiac activity. 



Osmotic Peessure of the Blood of Mtistelus canis under Normal 



Conditions 



Emphasis is often placed upon the constant value of the osmotic pres- 

 sure of mammalian blood. Yet Findlay ('05) calls attention to the fact 

 that there are diurnal variations in the osmotic pressure of human bloodT 

 Thus he gives the A of human blood at 9 a. m. as 0.535° ; at 12 m. as 

 0.558° ; at 1.30 p. m., after dinner, as 0.585°, and at 5.45 p. m. as 0.528°. 

 Bottazzi (^06) found that the A of the blood and body fluids of marine 

 invertebrates in the neighborhood of Naples fluctuated between 2.195° 

 and 2.36°. He also found a similar range in the depression of the freez- 

 ing point of the sea- water. Eodier ('00) working at Arcachon on the 

 southwest coast of France found that the A of the waters from the labo- 

 ratory basin varied between 1.87° and 1.95°, while the water from the 

 ocean itself was more constant, having A's ranging from 2.05° to 2.09°. 

 Eodier in describing the Bay of Arcachon said : "Its waters have a den- 

 sity, salinity and osmotic pressure always less than sea-water, and vary- 

 ing with the season, height of tide, place from which the water was taken, 

 depth of water and time of day." Eodier found that the freezing point 

 of the blood serum of different species of selachians was near to that of 

 their sea-water medium, although in many cases it was 0.04° to 0.05° 



