^4: ANNALS NEW YORK ACADEMY OF SCIENCES 



are two gateways between the internal media and the external medium, 

 namely, the gill membranes and the kidneys. After immersion of Miis- 

 telus in diluted sea-water, of course all movement of liquids in the case 

 of the kidneys must be from within outward; in the case of the gill 

 membranes the movement may be in both directions. 



Information has been gathered from the experiments as to the condi- 

 tion of the blood due to immersion of the fish in the modified sea-water. 

 In fresh water, the specific gravity of the blood is less than normal ; the 

 solids are 14.8 per cent less; the nitrogenous substances 15.6 per cent 

 less; the urea content has decreased 15.5 per cent; the chlorine content is 

 25.7 per cent less and the osmotic pressure has fallen 22 per cent. When 

 hypertonic saline solutions are introduced into the blood system of an 

 animal, one of the first reactions is the withdrawal of water from the 

 tissues into the blood ; but the present condition is the reverse. The 

 blood is deficient in salts. The tendency of the tissues will be to absorb 

 water from the blood. Evidence of this reaction has been presented on 

 page 52. But sufficient water cannot be taken into the tissues to coun- 

 teract the constant inflowing of water from the exterior. Even before 

 the tissues have begun to take up water, it is probable that the kidneys, 

 stimulated by the modified diluted blood, react in such a way as to cause 

 an increased secretion of water. The urine formed under these condi- 

 tions has a lower specific gravity, lower osmotic pressure and lower 

 chlorine content than the normal urine. Moreover, the quantity of urine 

 secreted is in excess of the normal quantity. It is possible that the ex- 

 cessive secretion of urine is due in the last analysis to an increased 

 amount of water in the blood flowing through the capillaries of the kid- 

 ney. If any considerable quantity of water has entered, there must have 

 been a readjustment of the caliber of the blood vessels, since no marked 

 increase in blood pressure can be detected. Baglioni called attention to 

 the fact that when almost all the blood was withdrawn from an elasmo- 

 branch Scyllium, in a short time the blood contained almost the normal 

 percentage of urea, although it had a lower osmotic pressure than nor- 

 mally. Moreover, he found that a starving Scyllium also exhibits a ten- 

 dency to retain its urea. It appears therefore that the cells of the kid- 

 ney are capable of retaining to a certain degree the urea as well as the 

 salts. It appears probable that the dog-fish possesses a mechanism for 

 the regulation of the osmotic pressure of its blood which is efficacious in 

 the case of slightly diluted external media. 



I have shown, however, that at the time of death of Must el u^ in fresh 

 water there is a deficiency of 15.5 per cent in urea and other nitrogenous 

 substances of the blood which I claim to be largely due to dilution of the 



