446 



BULLETIN OF THE BUREAU OF FISHERIES. 



decomposition of blood when drawn is a source of error which was guarded against. 

 Determinations made on samples which had been kept too long' are not included in 

 this report. The table of determinations is given below. 



Table IX. — Showing the depression of Ihefri ezing point produced by blood from marine salmon taken at 



Monterey, < 'al. 



L, 



These samples were taken from selected fish as they came in to the Packers' 

 wharf from the fishing grounds. All were medium and large fishes and were fresh, 

 some still giving signs of life. The minimal depression of the freezing point was 

 given by No. 31, —0.700 C; the maximal depression by No. 9, —0.811° C. The 

 mean depression of the series is —0.762° C, which represents a concentration of the 

 blood equivalent to a 1.26 per cent solution of sodium chloride, assuming a dissocia- 

 tion of 86 per cent at this concentration." The depression of the freezing point 

 produced by the sea water taken from the fishing grounds of Monterey Bay is 

 — 1.924° C. Compared with sodium chloride this concentration is the equivalent of 

 3.20 per cent, or two and one-half times the concentration of the salmon's own blood. 

 As a matter of fact the osmotic pressure of the sea water will be somewhat less, since 

 the dissociation of the different salts will be not quite so great as sodium chloride. 

 The fact I want to emphasize is obvious, namely, that the total osmotic pressure 

 remains far above that of the salmon's blood. 



The above showing justifies the conclusion that the thin epithelial layer of cells 

 which separates the blood in the gills from the surrounding sea water does not admit 

 of free diffusion of substances in solution in the blood on the one side and in the sea 

 water on the other. Respiratory exchange of oxygen and carbon dioxide takes place 

 through the gills between the blood and the sea water. The salts, however, can not 

 freelv pass. Even as diffusible a substance as sodium chloride is no exception to the 

 rule, the gill epithelium being impermeable to it. In the absence of a chemical 

 analysis of salmon blood, we may assume that the amount of sodium chloride present 

 is considerably less than that necessary to produce a depression of the freezing point 



"Interpolated from Ostwald's tables, Lehrbueh der Allgemeine Chemie, 2te Auf. 



