PHYSIOLOGICAL STUDIES OF THE CHINOOK SALMON. 455 



is not necessarily the inference. The absence of food and the important metabolisms 

 occurring during the eight to twelve weeks' sojourn in fresh water are to be consid- 

 ered in this connection, and possibly are sufficient to account for the change. 



The second consideration of the fall of concentration of the blood is in regard to 

 its effect on tissue metabolism and tissue life. Observations on vertebrates have 

 .shown that while the concentration of blood may temporarily vary sharply, owing 

 to the taking of water with the food or during abstinence from water and food, still 

 on the whole the concentration is remarkably constant, as Roth" has already empha- 

 sized. This constancy in physical condition, or isotonicity, is in fact regarded as a 

 prime physiological necessity for the normal life and activities of the tissues. 



The salmon undergoes a permanent alteration of 17.6 per cent, almost one-fifth, 

 ip the concentration of the blood, yet it is able to carry on vigorous activities of the 

 muscular and nervous systems, as well as those internal metabolisms which result in 

 the growth and development of the ovaries and testes and which involve a transfer- 

 ence of materials in large amount to these organs from other parts of the body, 

 especially from the muscles. The question may be raised, Is this decrease in the 

 proportion of solids in the blood really injurious; and if so, how far may it proceed 

 before death takes place? An indication of the limits to this process is given by 

 specimen No. 206, an old male too weak to keep off the retaining rack, from whence 

 1 removed it on Aug. 20, 1902. This salmon remained alive long enough to secure 

 a blood-pressure measurement. The serum depressed the freezing point by only 

 — 0.518 c C, representing a fall in concentration of 32 per cent in comparison with 

 blood from the marine salmon. Basing judgment on this single case, one would say 

 that a 32 per cent decrease in blood concentration represents the approximate limits 

 of blood dilution which will support the organized life of the individual. 



A reference table of the determinations of the freezing points made by different 

 observers on the blood and serum of divers species of animals is here presented. It 

 is not exhaustive, but represents the results given in the papers available, together 

 with some determinations of my own not previously published. Among the Selachii 

 and marine invertebrata, where the blood concentration follows closely that of the 

 sea water in which they live, obviously one must in making comparisons take the 

 environment into consideration. 



« Roth, Virehow'a Archiv, Bel. 1W, 1899, S. 488. 



