No. 599] OSMOTIC PRESSURE OF THE BLOOD 



651 



periments to test this ( '13) and found that when a change 

 was made in the external medium, though considerable 

 change took place in the blood of the dogfish, yet it was 

 considerably less than the external change. In fact it 

 appeared as though the change in the blood was roughly 

 proportional to the change in the external medium (p. 20, 

 Scott, '13). The condition was so marked as to show 

 clearly that the elasmobranch belonged in a category dif- 

 fering from that of the marine invertebrate. 



Third, the marine teleost. Much emphasis has been 

 placed upon the claim that these forms are absolutely 

 independent of changes in the external medium. With 

 this claim, I must differ. The following evidence is the 

 basis of this difference of opinion. In the first place 

 Tables I and II show that the blood of teleosts from the 

 Mediterranean has a higher osmotic pressure than that of 

 blood of teleosts from the ocean. There is a correspond- 

 ing though greater difference in the osmotic pressure of 

 the water. Dakin '08 in a trip from Kiel to Helgoland 

 found that the osmotic pressure of the sea water increased 

 7-t per cent, and that the osmotic pressure of the blood of 

 the plaice showed an increase of 20 per cent. The cod did 

 not show so great a difference, being but 4 per cent. 3 

 Garrey '05 reported A of the blood of the tautog at Woods 

 Hole to be 0.86° while at the New York Aquarium, where 

 the harbor water is much more dilute than at Woods Hole, 

 I found the a of tautog blood to be about 0.70°. There- 

 fore it would appear that even blood of the marine teleost 

 is somewhat modified by changes in the external medium. 

 And yet practical independence has been achieved. This 

 is evident from the fact that the marine teleost lives in a 

 medium which has an osmotic pressure over twice as 

 great as that of the blood of the fish. 



Macallum ( '10) has explained the peculiar osmotic pres- 

 sure of the blood of marine teleosts as due to their origin 

 from fresh-water teleosts. This is based on morpholog- 



3 On the other hand Dekhuyzen, '05, found a difference of 20 per cent, 

 in the osmotic pressure of cod blood according to the locality from which 

 the fish was taken. 



