SCOTT, STUDY OF CHANGES IN MLSTELUS CANIS CA 



of its blood pressure. This fell 30 per cent from its value at the begin- 

 ning of the experiment. The fall was gradual. The heart was beating at 

 the rate of 16 per minute at the beginning of the experiment and 8 per 

 minute at the end. Eespirations were at the rate of 14 per minute at the 

 beginning and ceased about four hours after fresh water had been turned 

 on. Fig. 13 shows the character of the changes in blood pressure and 

 heart beat in this specimen. The absence of the spasmodic respiratory 

 movements is apparent. Other spiny dog-fishes at the New York Aqua- 

 rium did not withstand the immersion for so long a time. But in every 

 case with Squalus the changes in blood pressure, respiratory rate and 

 heart beat took place much more slowly than was the case with Mustelus. 

 There are two factors that may have a causal connection with this differ- 

 ence. In the first place, because of its immersion in diluted sea-water 

 during its stay in the aquarium, Squalus may have acquired a certain kind 

 of immunity to the freshened water, so that a transition to wholly fresh 

 water would not have such a quickly fatal effect as in the case of Mustelus. 

 That the factor is not altogether the change in the osmotic pressure of 

 the blood is suggested by the fact that after about an hour^s immersion in 

 fresh water the A of the blood of a number of spiny dog-fishes, as has 

 been shown on page 33, was about the same as that of Mustelus, although 

 it must be confessed not quite so high. In the second place, the tempera- 

 ture of the water in which the spiny dog-fishes had been kept as well as 

 that of the fresh water in which the fishes were. immersed in the experi- 

 ment was low, the latter being 12° C. Metabolism was probably at a low 

 ebb, and therefore chemical and physical changes would take place more 

 slowly. 



In publishing blood pressure tracings from the Chinook salmon, Greene 

 (^05) states that certain waves, which are shown, are due to the rhythmi- 

 cal effect of respirations on the blood pressure which also records heart 

 beats. A series of waves similar to those published by Greene are now 

 and then found in the normal blood pressure tracing from Mustelus as 

 shown by Fig. 10-1. In this case, it is certain that the waves are not all 

 synchronous with the respirations, nor have the respirations anything to 

 do with them. On the contrary, these are evidently Traube-Hering waves 

 and probably due to rhythmical variations in the tone of the vaso-motor 

 center. Almost as many respiratory movements take place during each 

 of these rhythmical periods as there are heart beats recorded. It may be 

 that the waves in this case are due to the destruction of the spinal cord. 

 All indications of them cease when the animal is placed in fresh water. 



That the heart action is not altogether dependent upon respiratory 

 activity is shown by the fact that the heart continues to beat long after 



