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ANNALS NEW YORE ACADEMY OF SCIENCES 



respiration has ceased. The respiratory rate may suddenly increase tem- 

 porarily, while the heart rate is steadily declining. On the other hand, 

 the heart rate may become more frequent while the respiratory rate is 

 declining. 



Parker ('10) stated "that the rate of gill movement in the dog-fish 

 depends upon the momentary state of movement of the animal. When 

 resting, they vary from 35 to 40 movements per minute. When swim- 

 ming slowly, they respire 50 to 55 times 

 per minute. In vigorous swimming, the 

 rate is doubtless still more rapid." The ac- 

 companying figure. Fig. 14, is a record of 

 the respiratory and cardiac activity taken 

 simultaneously, and shows that while the 

 respiration rate is 52 per minute the heart 

 rate is but 40 per minute. At times, the 

 two rates may be equal; but this is rather 

 the exception, so far as my observation 

 goes. The two seem to be independent. 



We may conclude that the respiratory 

 convulsions described above do not produce 

 cardiac spasms as shown in Fig. 12, but, 

 on the contrary, the two processes occur 

 simultaneously and both have the same 

 cause. 



We know that the density of the water is 

 changing constantly, but these spasmodic 

 movements occur long after the water be- 

 comes fresh. The movements cannot be 

 Fig. 14. — Comparative rate of res- due to the stimulus of changing external 



piration and heart heat in Mus- -, ., f^j i i n i ji j* 



telus in sea-water. Upper trac- density. A\ e knOW, toO, that the OSmotlC 



ing, heart heat, 1,0 per minute; pressure of the blood is changing con- 



heJow this, respiratory, rate, 52 , ,-, -1111 i i- i 



per minute stantly ; indeed, the change continues long 



after the water has become fresh and con- 

 tinues to change up until the death of the animal. Owing to swelling 

 corpuscles, dilution of the blood and alterations in the gill membranes, 

 it is probable that the blood fails to get oxygenated and that its CO2 in- 

 creases in quantity. In fact, the blood drawn from the caudal artery at 

 the end of the experiment has a dark appearance, brightening upon ex- 

 posure to the air. If thus the blood becomes profoundly venous, laden 

 with CO2 it would flow through the respiratory center and cause spas- 

 modic contractions of the respiratory muscles. 



