SCOTT, STUDY OF CHANGES IN MUSTELUS CANIS 37 



by the dilution due to the entrance of water into the blood and that this 

 might be a contributing cause of death. In fact, Mosso ('90) working at 

 Naples made this the basis of his explanation of the death of elasmo- 

 branchs under this condition. The freezing point of the sea-water from 

 the Mediterranean is about 26 per cent lower than that of the water at 

 Woods Hole. The degree of change to which the fishes were subjected 

 when placed in fresh water was therefore greater in the case of the fishes 

 with which Mosso worked. This difference may account in part for the 

 divergence of my results from those of Mosso. Mosso stated that, if the 

 tail of Scyllium was cut off after the fish had been in fresh water for half 

 an hour, no more blood flowed from the artery, while the heart still con- 

 tinued to beat. On the other hand, I found that blood might be obtained 

 from the caudal artery of Mustelus up to the point of death in fresh 

 water, i. e., from one to two hours. Mosso also claimed that the serum 

 remained almost normal at the time of death in fresh water. We have 

 here noted a profound lowering of the osmotic pressure of the serum. 

 The results obtained by Garrey ('05), Dakin ('08) and myself shoAV that 

 this statement of Mosso's cannot be correct. Mosso believed the real 

 cause of death to be due to suffocation. By the action of the fresh water, 

 the red blood cells go to pieces and clog up the capillaries of the gills, 

 thereby cutting off the exchange of gases in these structures. 



Following up this hypothesis, Mosso studied the osmotic resistance 

 which the red cells offered to different salt solutions. For example, the 

 erythrocytes of selachian blood were destroyed in 2.5 per cent solutions 

 of sodium chloride and the fluid soon became red. Teleosts like Conger 

 and Murcena had a greater resistance and first lost their haemoglobin in a 

 0.3 per cent NaCl solution. Mosso found that fresh water forms possessed 

 blood more resistant to salt solutions of different dilution than marine 

 teleosts, while anadromous fishes like Anguilla and Acipenser possess 

 blood cells which are especially resistant to dilute salt solutions. 



On account of the divergence between my observations and those of 

 Mosso, I concluded to ascertain whether at the time of death as the result 

 of immersion of Mustelus in fresh water its corpuscles were laked. This 

 was ascertained in the following way : The spinal cord of a dog-fish taken 

 from sea-water was destroyed. About ten cubic centimeters of blood were 

 drawn from the caudal artery. This was closed, and the fish was trans- 

 ferred to sea-water which was rapidly changed to fresh. Near the time 

 of death, the artery was opened a second time and a second sample of 

 blood was obtained. Soon after each sample of blood was taken, it was 

 defibrinated. Then each was placed in a separate centrifuge tube and the 

 two were simultaneously centrifuged. At the end of this process, the 



