SCOTT, STUDY OF CHANGES IN MUSTELUS CANI8 H 



In both of the solutions more concentrated than sea-water there is a 

 lowering of the freezing point of the blood, an effect which is just the 

 opposite of that produced by fresh and dilute solutions. The initial effect 

 is greater in the more concentrated solution, although the final effect is 

 about the same. 



Although in each of the five experiments the normal A of each speci- 

 men as taken from sea-water is not known, the results indicate that the 

 degree of change in the osmotic pressure of the blood depends upon the 

 molecular concentration of the external medium. The results differ from 

 those of Fredericq, in that they show that the osmotic pressure of the 

 blood does not become equal to that of experimental media that differ 

 markedly from the medium to which the animals are normally adapted. 

 Attention is again called to the different degree to which the individual 

 animals respond to modifications in the concentration of the external 

 medium. Some die sooner than others in these abnormal media. Hyde 

 (^08) observed that the effects of operation varied in different skates. 

 For example, Hyde noted that when the same operation was performed 

 upon two animals apparently in every respect alike, in the one case the 

 effects might be momentary, while in the other they might be severe and 

 prolonged. 



CHANGES IN THE OSMOTIC PRESSURE OF THE BLOOD FROM THE NORMAL 

 CONDITION UNTIL NEAR DEATH IN FRESH WATER AND CONCENTRATED 

 SEA-WATER 



Green (^05) found that the chinook salmon, Oncorhynchus tschaw- 

 ytscha, in its migrations to the head waters of rivers for spawning, under- 

 went a permanent decrease of 17.6 per cent in the concentration of its 

 blood and yet was able to carry on with vigor the activities of its mus- 

 cular and nervous system. How far may this decrease proceed before death 

 takes place ? He found that the blood serum of an old weak male salmon 

 showed a decrease of 32 per cent from the mean A of the blood serum of 

 normal salmon. This represents the maximum of dilution of which the 

 blood is capable while still maintaining life. I concluded to investigate 

 this question in the case of the dog-fish, Mustelus, and at the same time 

 to study the progressive osmotic changes of the blood from normal life to 

 death in fresh water and concentrated sea-water. Cessation of breathing 

 was taken as an index of death. 



The following technique was employed : The spinal cord of the animal 

 was exposed from the dorsal aspect, at the junction of the caudal fin with 

 the trunk of the body. In this way no large blood vessel was interfered 

 with. The cord was then destroyed by a probe as far forward as the an- 



