RESPIRATION BY THE SKIN. 



723 



A series of experiments by Pembrey l has shown that the effect of 

 age upon the respiratory exchange must be considered in relation to the 

 temperature of the external air and the stage of development in which 

 the animal is at birth. Animals born in a condition of advanced 

 development, like that of guinea-pigs and chickens, have a respiratory 

 exchange which is relatively two or three times greater than that of 

 the adult. Animals born in a helpless state, like that of mice and 

 pigeons, have at the ordinary temperature of the air a metabolism 

 relatively smaller than that of the adult ; but with a rise in the 

 external temperature towards the temperature of the body the re- 

 spiratory exchange increases towards the value in the adult. These 

 differences, which are intimately connected with the temperature of 

 the animal, are discussed more fully in other parts 2 of this work. 



EESPIRATION BY THE SKIN AND ALIMENTARY CANAL. 



Cutaneous respiration of amphibia. In many of the lower animals 

 the exchange of gases between the skin and the surrounding air or water is 

 considerable, and in some of the amphibia is equal to, or even greater than, that 

 effected by the lungs. As early as the end of the last century, Spallanzani 3 

 showed that many amphibia could readily take up oxygen and discharge 

 carbon dioxide after their lungs had been removed, and that in this condition 

 they lived longer than animals of the same species whose skin had been 

 covered with varnish. These observations were extended by Edwards, 4 

 who found that frogs deprived of their lungs would live a long time, provided 

 that the external temperature was low. This cutaneous respiration took place 

 as readily in flowing water as in air, for normal frogs could be kept alive 

 although never allowed to come to the surface, provided that the temperature 

 of the water did not exceed 12; the cutaneous respiration was sufficient for 

 the small amount of metabolism which occurred at low temperatures. Kegnault 

 and Eeiset 5 found, by direct experiment, that frogs absorbed as much oxygen 

 and discharged as much carbon dioxide after, as before, removal of their 

 lungs. The following figures give their results : 



1 Jo-urn. Pliysiol., Cambridge and London, 1895, vol. xviii. p. 363. 



2 See " Animal Heat," this Text-book, vol. i. 



3 "Memoires sur la respiration," trad, par Senebier, Geneve, 1803, pp. 72, 114. 

 "De 1'influence des agens physiques sur la vie," Paris, 1824, pp. 12, 41-62. 



5 Ann. de cTiim. etphys., Paris, 1849, Ser. 3, tome xxvi. p. 506. 



