1 24 RESPIRA TION 



In sleep, because the metabolism is lessened, the rate is less; the 

 decrease in muscular activity during sleep probably helps the effect. 

 The decrease is, on the average, about 20 per cent, of the waking rate. 

 Finally, posture may affect the rate aside from the variations of muscular 

 exercise in the different postures. In standing, the respiration is faster 

 than in sitting, and faster in sitting than in lying down. This, perhaps, 

 is due to mechanical interference with the depth of the inspirations, 

 which, as we noted above, increases the rate. 



The breath-rate varies widely in different animals, and a tabulation of 

 the rates of many genera gives little clue to the reason for some of the 

 variations. 



BREATH-RATES OF VARIOUS ANIMALS (BERT). 



Complete Respirations per Minute. 



Hippopotamus .... I Panther 18 



Snake 5 Canary 



Tiger 6 Cat 



Condor 6 Pigeon 



Rhinoceros . . . . 6 to 10 Moliusca 



Ass 7 Perch . 



Giraffe 8 to 10 Hippocampus .... 33 



Lion 10 Raja . 



Jaguar 11 Eel 



Dromedary 11 Torpedo 



Horse 10 to 12 Rabbit 



Tortoise . 12 Mullet 



. 18 

 . 24 

 . 30 

 14 to 65 

 30 



50 

 50 

 51 

 55 

 60 

 90 

 100 



Crab . 12 Sparrow 



Dog 15 Siskin . 



Ox 15 to 18 Rat (asleep) 100 



Man 18 Rat (awake) . . . up to 210 



Why the rhinoceros should breathe, say, eight times as often as the 

 hippopotamus, or the sparrow five times as frequently as the canary, it is 

 difficult to satisfactorily explain. The physiology of other differences is 

 obvious, and leads to rather fundamental considerations of importance. 

 The most basal criterion of difference is probably that of difference in 

 degree of the body-metabolism based either on difference in the activity 

 of the animal or on its size. Moreover, the heat lost is determined 

 largely by surface in ratio to mass, or as square to cube, which, of 

 course, gives the smaller animal the larger proportional surface, and so 

 the larger proportional loss of energy. More oxygen is needed to cor- 

 respond to this additional metabolism. The same explanation probably 

 applies to the difference in the respiratory ratio of the cat and the tiger, 

 two felines much alike save in size. The difference in rate of the rat's 

 breathing and in that of the tortoise is largely one of metabolism, arising 

 from inherent differences in habits and nature, the rat being active and 

 homothermous, the tortoise " cold -blooded" and proverbially slow. In 

 general the breath -rates of the birds are high because of their lively 

 metabolism, which is dependent in turn on their great bodily activity. 

 In the case of the condor, however, a bird at once large and lazy, we 

 see a very low rate, on the principles already suggested. 



Special Functions Connected with Respiration. There are a number of 

 complex processes, variously useful, and more or less normal, which 



