PHYSIOLOGICAL SIT DIES OF THE CHINOOK SALMON. 



449 



Table XI.— Depression nfthi frei zing point produced by blood and serum from salmon taken on the McCloud 



River, Baird, ' 'al. 



The mean or average depression of the freezing point produced by the blood of 

 salmon from the spawning beds, as shown by the above table, is —0.628° C, a figure 

 that shows a marked falling off in the concentration of the blood when spawning 

 salmon are compared with salt-water and tide-water salmon. The variation in the 

 spawning-ground salmon is very great, as is to be expected when the probable gnat 

 difference in time spent in fresh water is taken into consideration. Many salmon 

 arrive on the beds during the spawning time in fine flesh and full vigor, while others 

 which have been on the grounds for a longer time show unmistakable external signs 

 of decreased energy and vitality. Such fish have a less concentrated blood and their 

 tissues are notably less firm than is the case with fresh arrivals. The extremes of 

 concentration of whole blood measured at Baird hatchery are Nos. 212 and 61, with a 

 depression of the freezing point of — 0.557 c and — 0.705 c (_'., respectively. No. 212 

 was an artificially spawned female that was in thin flesh: No. 61 was a large prime 

 male whose muscles were still pink and firm, a fish in full vigor. The larger number 

 of samples of serum show an average depression of the freezing point of —0.613° C. 

 which varies from the mean taken from whole blood determinations by about 2? 

 per cent only. If we consider only the 14 fish in which measurements were made 



