SCOTT, 8TUDY OF CHANGES IN MUSTELU8 CANIS 53 



Fischer ('10) found that if a ligature was tied about a frog's leg and the 

 animal was put into fresh water the leg became greatly swollen because 

 of the absorption of water. The circulation of the blood and lymph being 

 stopped by the ligature, the kidneys could not pass off the excess of water. 

 Will the kidneys of Mustelus act in the presence of the diluted blood in 

 such a manner as to conserve the normal osmotic pressure of the blood ? 



Observations were made by Dr. W. Denis and the author on the quanti- 

 tative secretion of the urine of Mustelus. The method of collection has 

 been described by Denis ('12). The average secretion of urine per Si- 

 hour period was 21.6 c. c. The urine does not appear to be eliminated 

 constantly but periodically, as in the case of the higher forms. Since 

 Mustelus dies in about an hour after immersion in fresh water, no at- 

 tempt was made to collect the urine during such a short period. The 

 effect of four other solutions, however, the osmotic effects of which have 

 already been shown, were tried : namely, sea-water ; concentrated sea- 

 water having a A of 2.60° ; three-fourths sea-water plus one-fourth fresh 

 water; and one-half fresh water plus one-half sea-water. For the first 

 few hours after immersion the average secretion per hour for four speci- 

 mens in sea-water was 0.4 c. c. urine ; in the concentrated solution of sea- 

 water, the average secretion of two fishes was 0.2 c. c. urine ; in the solu- 

 tion of three-fourths sea-water plus one-fourth fresh water, the average 

 secretion of two fishes was 1.2 c. c. urine ; and in the solution of one-half 

 sea-water plus one-half fresh water, the average secretion of five fishes 

 was 1.4 c. c. urine. The results show that, in the concentrated solution 

 of sea-water, less urine, and, in the dilute solutions, more urine is secreted 

 than in normal sea-water. There is no doubt then that the immersion of 

 the fish in modified solutions of sea-water with the resulting changes in 

 the molecular concentration of the blood, causes an immediate reaction 

 on the part of the kidneys. 



The nature of the urine thus secreted as compared with normal urine 

 is shown by the results of the following experiments : The A's of the urine 

 collected from three dog-fishes immersed in sea-water were respectively 

 1.69°, 1.70° and 1.77°. The average of these values is 1.72°. These 

 results indicate that it may be h}^otonic and not isotonic with the blood. 

 Bottazzi ('06) stated that elasmobranch urine is isotonic with the blood, 

 although some of the results given by him indicate that it is hypotonic. 

 The A of the urine collected from a dog-fish immersed in a solution of 

 one-half sea-water plus one-half fresh water for about four hours was 

 1.61°. Furthermore, the specific gravity of two samples of normal urine 

 was found to be 1.034 and 1.037, while that of two samples of urine col- 

 lected after immersion of two fishes in one-half sea-water plus one-half 



