SCOTT, STUDY OF CHANGES IN MU8TELUS CAN IS 23 



It is clear that, after immersion in fresh water, we get as before a rise 

 in the freezing point of the blood. After the return to sea-water, the A is 

 lowered and the osmotic pressure is increased again ; but the normal os- 

 motic pressure of the blood is not regained, even though the return to 

 sea-water is as long or even longer than the sojourn in fresh water. This 

 is shown in the case of the fourth specimen; for after 25 minutes in 

 fresh water the freezing point had been raised 0.24° above normal, but 

 when the fish had been returned to sea-water for 100 minutes the freez- 

 ing point was still 0.12° above normal. Figure 5 shows the changes in 

 the A of the blood of this specimen. The fish was in fresh water from 

 F to F^ and in sea-water from F^ to S. The base line represents the 

 normal A ; the abscissas, time in minutes, and the ordinates, the rise in 

 the freezing point of the blood. At first one might conclude from these 

 experiments that the limiting membranes were not as permeable in one 

 direction as the other. A second experiment of this nature will be de- 



+0.20 



f - -- - - -- — 1^' 



Fig. 5. — Changes in A of Mood of Mustelus due to immersion in fresh tvater followed 



hy return to sea-water 



scribed. In this case, the mixed blood of the two specimens was used for 

 the determination of the normal A, 1.895°. After 75 minutes' immersion 

 in fresh water, there was noted a rise in the freezing point of the mixed 

 blood of 0.245°. Both specimens were then returned to sea-water and 

 one died soon after. A determination was made from the blood of the 

 other 225 minutes after the return, and its A was 0.05° above the normal 

 A. Although there was an apparent return to the normal condition, the 

 animal was injured in some way, for it died soon after. In fact, it is not 

 quite correct to assume that the normal condition of the blood was re- 

 gained for the last figure given, i. e., 0.05° is obtained by subtracting the 

 final A of the blood of this fish from the A of the mixed blood of this fish 

 and the other which died earlier. The number of molecules and ions in 

 solution in the blood had decreased after immersion in fresh water. Cer- 

 tain parts normally present had escaped into the surrounding medium. 

 The return of the organism to its normal medium did not suffice for the 

 return to the blood plasma of the normal quantitative relation of parts in 

 solution. 



Concentrated solutions were also tried. Two such experiments will be 



