3 ANNALS NEW YORK ACADEMY OF SCIENCES 



the sea-water in which it lives. It has already been noted that Rodier 

 ('00) observed the same fact in connection with the elasmobranchs at 

 Arcachon. The observations of Bottazzi ('06) reveal the same relation- 

 ship. Finally, Garrey's '05 data agree nearly with mine. 



The small difference between the A of the blood and that of sea-water 

 is important in that the molecular concentration of the blood of elasmo- 

 branchs is only approximately equal to that of the sea-water. According 

 to the above table, the blood of Mustelus can pass with entire safety 

 through a range of at least 0.15° in its osmotic pressure. 



Changes in the Osmotic Pressure of the Blood due to Alterations 

 IN THE Density of the External Medium 



PRELIMINARY STUDY 



It has been shown by a number of investigators that the osmotic pres- 

 sure of the internal body fluids of the marine invertebrates depends upon 

 the molecular concentration of the surrounding medium. Fredericq 

 ('04), Garrey (^05) and Dakin (^08) have shown that this is true to a 

 certain degree of the elasmobranchs. Fredericq concluded that a new 

 equilibrium was established when he put Scyllium into diluted or con- 

 centrated sea-water. For example, he put Scyllium into diluted sea-water 

 having a A of 1.67° for twenty-seven hours, at the end of which time the 

 A of its blood serum was 1.70°. Another specimen was put into concen- 

 trated water having a A of 2.72° for twenty-four hours, when the A of 

 the blood was 2.70°. Garrey ('05) found that the blood of Mustelus 

 cams, though normally having a mean A of 1.88°, changed to 1.45° ^fter 

 an hour's immersion in fresh water. Dakin ('08) found that when the 

 spiked dog-fish, Acanthias vulgaris, and the skate, Raia clavata, were put 

 into fresh water, there was a considerable fall in the osmotic pressure of 

 the blood. The mean A of these forms was 1.90°. In the four hours dur- 

 ing which the dog-fishes were in fresh water, the A of the blood changed 

 to 1.435°, showing a rise in the freezing point of 0.465° from the normal- 

 condition. The three specimens from which the above results were ob- 

 tained were nearly dead at the end of the experiment. The change in the 

 blood of the skate was not as great. This form was nearly dead at the 

 end of two hours' immersion in fresh water, at which time the A of the 

 blood was 1.645°, showing a rise in the freezing point of .255°. In these 

 experiments of Garrey and Dakin, death took place before a new osmotic 

 equilibrium was established. I determined to ascertain whether there 

 was any relation between the duration of immersion in modified solutions 

 of sea-water and the change in the osmotic pressure of the blood. The 

 form used was Mustelus canis. As brought into the laboratory, the fish 



