No. 497] THE BUREAU OF FISHERIES 



339 



can likewise be investigated by determining whether the 

 freezing point of blood serum from a fish which has been 

 kept in fresh water is higher than that of blood serum 

 from a fish taken from its normal medium. Although 

 experiments of this sort had already been performed by 

 a number of competent investigators, it seemed worth 

 while to make the test again. This was impossible to do 

 in the case of Fundulus on account of the small amount 

 of serum obtainable. The experiment was carried out, 

 however, upon Mustelus canis, the "smooth dog-fish." 9 

 Five determinations were made with the blood serum of 

 fishes taken from normal sea water, and five with blood 

 serum of fishes that had been kept in fresh water for 

 an hour. These experiments agreed in showing that the 

 freezing point of serum from fishes kept in fresh water is 

 much higher than that of fishes taken from sea water. 

 It was thus demonstrated that the blood of fishes may be 

 diluted by a sojourn in fresh water, and support is given 

 to the view that the change in the number of corpuscles 

 counted was due to dilution or concentration of the blood. 

 The last mentioned experiment upon Fundulus, in which 

 distilled water was used, suggests that after the first dilu- 

 tion of the blood, due to the physical process of osmosis, 

 there occurred a physiological reaction on the part of the 

 organism, the excess of water being expelled from the 

 blood. That it remains in the body of the animal, how- 

 ever, is shown by the persistent increase in weight. 



Francis B. Sumner, Ph.D., director U. S. Fisheries 

 Laboratory, Woods Hole, Mass.— (1) The supervision of 

 the biological survey; (2) experiments in the deaeration 

 of the local salt-water supply; (3) an investigation into 

 the meaning of the color variations of Litorina pallia t a 

 Say (carried on jointly with James W. Underwood). 

 The first two of these lines of investigation have already 

 been discussed in the more general part of the paper; a 



' The known physiological differences between elasmobranchs and teleosts 



