70 ANNALS NEW YORK ACADEMY OF SCIENCES 



esses of association and dissociation with the constituents outside of it. 

 Such association is in the nature of more or less stable chemical combi- 

 nations which he terms adsorpates. For each cell there is a range of 

 osmotic pressure within which partial association and discussion is pos- 

 sible, and within this range labile exchanges are possible. 



This idea may be extended to explain why the tissues of the dog-fish, 

 though normally adapted to an osmotic pressure of its blood approxi- 

 mately equal to that of the sea-water, is able to \i\e in the dilute sea- 

 water of New York harbor. In such dilute water, the blood has an os- 

 motic pressure represented by a freezing point of — 1.70°. This repre- 

 sents the lowest osmotic limit of the blood at which the cells of the dog- 

 fish can establish proper associations with the substances in the blood, or 

 in other words at which the metabolic processes can take place. It is of 

 interest to note that this freezing point, namely, — 1.70°, is also the least 

 noted in the case of the smooth dog-fish, Mustelns, at Woods Hole (see p. 

 7). Continuing Moore's conception, it is probable that — 1.87° repre- 

 sents the optimum osmotic pressure at which the labile processes of asso- 

 ciation and dissociation can most perfectly take place. Greene ('05) im- 

 plies the same idea, for he concludes that salmon having blood with an 

 osmotic pressure widely different from the mean are in a pathological 

 condition. Dakin ('08), Dekhuyzen ('04) and others who have deter- 

 mined the freezing points of teleost blood seem impelled to insist on its 

 constancy; yet considerable variation appears in the actual results noted 

 by them. Variations occur even in human blood at different times of 

 day, as shown on page 6. Winter ('96) has maintained that metabolic 

 processes would cease if the osmotic pressure of the blood should attain a 

 stagnant dead level. 



It should be observed in this connection that the freezing point of the 

 blood of the dog-fish at the New York Aquarium remains at about 

 ■ — 1.70°, while the water in which they live has a freezing point of about 

 — 1.00°. The animal is able to prevent a further lowering in the osmotic 

 pressure of the blood. It cannot resist perfectly the change in the os- 

 motic pressure of the external medium, but it is able to carry on life 

 processes at the lower limit. It is possible to conceive that because of the 

 dilute condition of the blood, the cell finds great difficulty in establishing 

 normally stable associations. Life processes are continued, but with de- 

 creased efficiency. Indeed observation shows that the elasmobranchs at 

 the New York Aquarium are less vigorous and hardy than those at Woods 

 Hole. 



The blood of the fishes living at the lower limit, namely, having a 

 freezing point of — 1.70°, is not as dilute as the blood of Mustelus at the 



