18 



ANNALS NEW YORK ACADEMY OF SCIENCES 



-020 



■1.40 



normal condition until near the death of the animal in the above concen- 

 trated solution. Since the curve shows a progressive lowering of the 

 freezing point of the blood, it should be interpreted as showing an in- 

 crease in the osmotic pressure of the blood. There is a slight falling off 

 in the effect after an initial sudden change in the freezing point. Toward 

 the end of the time of immersion the change is more rapid again. 



There is good evidence for believing that the dog-fishes in their migra- 

 tions up and down the coast wander into brackish waters. The organism 

 must be adapted therefore to withstand a moderate amount of decrease in 

 the density of the external medium. Under natural conditions, however, 

 the organism is never subjected to such a concentrated solution as was 

 used in the present experiment. The concentrated salt solution may act 



as a chemical stimulus upon 

 the arterioles of the gills, caus- 

 ing them to dilate, and thus 

 bringing about a greater influx 

 of blood to the gills, from the 

 capillaries of which the blood 

 would lose water rapidly by 

 osmosis. After the initial 

 Fig. 2.-cha,we in A of blood of Musteius due stimulus, the arterioles would 



to immersion of fish m a hypertonic solution 



of sea-water until death. recover their tone, there would 



be a decreased amount of blood 

 sent to the gills and the loss of water would be retarded. The more 

 rapid increase in A toward the end of the period is evidently an index of 

 greater changes in the physico-chemical constituiion of the organism. 



The above results as to the effect of fresh water and concentrated sea- 

 water on the osmotic pressure of the blood show that, at the time of death 

 in fresh water, there is an average rise in the freezing point of the blood 

 of 0.41° and, at death in the above concentrated solution, a fall of 0.24°, 

 i. e., in the osmotic pressure a reduction of 21.9 per cent and an increase 

 of 12.8 per cent respectively. The values probably represent the lethal 

 limits of departure from the normal constitution of the blood within 

 which protoplasmic activities of this form take place. I must differ from 

 Fredericq and others who would classify the elasmobranchs with the ma- 

 rine invertebrates as to the osmotic relations of their body fluids to the 

 external medium. This conception would imply that the degree of 

 change in the osmotic pressure of the blood is equal to the degree of 

 change in the osmotic pressure of the external medium. In the case of 

 Musteius, we have seen that this is not true. It may be, however, that 

 some relationship exists between the osmotic pressure of the blood of the 



