53 



its im.ii'T'ncity. 



In presenting cert-iin of the more specific opportunities open to 

 marine physiology) we may for convenience cItss these under two 

 headings: (a) those phases oest att?cked vi'^ the r-^letionship 

 between the tissue and the blood or lymph, and (b) that between the 

 protoplasm of the cell -^tnd its immrdiate -nvironm nt. 



Under the first of these subdivisions th'i applic^-tion to the 

 comparative physioloey of m•^rine animals of the methods now practiced 

 in the investigations of the respiratory, circul-tory ^nd blood 

 physiology of mrm offers a most promising field. An emminent 

 physiologist, indeed, gives it as his opinion that this is one of 

 the great scientific opportunities of the coming holf-c rntury ; and 

 that voyages of well equipped expeditions, making use of experimrntal 

 methods of this kind, promise to put the natural history of the sea 

 on a new level. 



Thus, to take perhaps the most obvious example, we know very 

 well that the ■' istribution of marine animals, in fact their whole 

 economy, is largely controlled by temperature. All of them have an 

 optimum range within which they live, with lethal limits above and 

 below. But in many cases the v-getative metaoolic activities (ex- 

 pressed as growth) and the reproductive proceed most successfully at 

 different temperatures - witness the growth of the lobster to large 

 size in cold water, but the inability of its larvae to survive at all 

 except in warm. 



The ciuestion ho^ this temp-^-rature control works on the internal 

 activities is now to the fore. Is this a simple matter of difference 

 in the rates of the chemical reactions involved (for certainly the 

 m.etabolic rates do vary with temperature) or is something more at 

 work? 



Study of the effect of temp.-rature on the respiratory processes 

 of various m.arine animals also offers a fertile field, and a very 

 attractive one, because this effect is srreat enough to render tissues 

 that are adapted to the harmonious exercise of respiratory functions 

 (i.e. to the transport of oxygen) at on- temp-rature quite worthless 

 at another, no m.atter how much oxygen there may be dissolved in the 

 water. A study of the temperature factor in this relation m.ay 

 contribute to an understanding of the thermal control of geographical 

 distribution. May this, for example, be one cause of the'^great 

 diffrrences in thermal requirements between closely related species - 

 or between geographical races of a given species, such as we know to 

 exist among the cod fish and the herring, which find their optimum at 

 one temperature in one region, at another temperature in another? 

 In the Straits of Brlle Isle, for example, the cod prefer and seek 

 much lower temperatures than they do on Nantucket Shoals. 



Especially intriguing in this connection are the specific 

 properties of the respiratory proteins as determinants of the 

 pressure of oxygen gas- in "he blood. In fact, the whole ouestion of 

 the oxygen reouiremients of different animals and of the same animal 

 at different temperatures is little understood. Wh^t, for instance, 

 is the diffTjrence between the blood of active fishes and molluscs, 

 such as trout and squid, and that of their more slus-gish relatives, 

 and the d if fere "ice between the tissues that perform^respiration among 



