CRYOSCOPIC AND OSMOTIC DATA. 83 



to either side of those isosmotic with the sea waters of our coast 

 laboratories. 



(b) Magnesium Chloride. — In solutions of this salt some of 

 the molecules are dissociated into three ions, which accounts 

 for the fact that the osmotic pressure is greater and consequently 

 the depression of the freezing point is lower, than that of equi- 

 molecular solutions of sodium chloride. The following commonly- 

 employed solutions have been tested (cf. Table V.). 



Animals. 



In addition to data previously published by the author (loc. 

 cit., p. 263), several determinations have been made on the blood 

 of animals of the waters of the American coast, and inland rivers. 



(a) Limulus polyphemus. — In the work referred to it was 

 shown that under experimental conditions the blood of this 

 animal, like that of other marine invertebrates varies to conform 

 in concentration to that of the external medium. We have 

 since found that this is true in the natural habitat of these ani- 

 mals, thus at Woods Hole (1904) the blood of Limuli depressed 

 the freezing point like sea water, to — 1.82° C. At Beaufort, 

 N. C, July 20, 191 1, the water of the Fisheries "pound" froze 

 at — 2.03° C. The blood of four Limuli taken from this water, 

 in which they had been kept for several weeks, showed the fol- 

 lowing freezing points, respectively, — 2.025°, — 2.03°, — 2.04° 

 and — 2.35° C. In the case of another Limulus captured at 

 "Cross Rocks" in the Newport River, near Beaufort, September 

 8, 191 1, the blood A = — 1.71° C. while the water at that 

 place depressed the freezing point to — 1.707° C. Such readings 

 taken from animals under natural conditions established the 

 absolute identity of osmotic pressure of the external and internal 

 media despite the differences in their composition. 



(b) Elasmobranchs. — A shark seven feet in length (not identi- 

 fied) was captured in the Fish Commission nets at Beaufort, 

 July 27, 191 1 ; the sea water froze at — 2.02° C; cryoscopic 

 readings of the blood from the heart and portal vein, withdrawn 

 immediately after death, were identical, within 0.01° C, and 

 showed A to be — 2.182° C, which again is practically identical 

 with that of the Beaufort sea water taken in the neighborhood 

 of the fish trap on that date. 



