VIII THE VOCAL AND RESPIRATORY ORGANS 



175 



conditions. If carbon dioxide is prevented from escaping 

 through the skin, more of it will be exhaled through the lungs, 

 or if the lungs are tied, more carbon dioxide will be eliminated 

 through the skin. 



The relation between the cutaneous and pulmonary respi- 

 ration of the frog has recently been quite exhaustively studied 

 by Krogh. The lungs were supplied with air by means of 

 artificial respiration, and the income of oxygen and the out- 

 put of CO2 from both the lungs and skin compared under 

 various conditions. In Raiiafiisca at a temperature of 20° C. 

 the average ratio of oxygen income to COo output in several 

 experiments on frogs taken at different times of year was, 

 in pulmonary respiration, Oo 105 : COo 45 ; in cutaneous 

 respiration O2 52 : COo 129. It is thus evident that in the 

 lungs the oxygen taken in is greatly in excess of the COo 

 given out ; while in the skin the reverse relation obtains. In 

 Rana esculenta relatively more oxygen is taken in through 

 the skin and relatively less CO2 eliminated through the lungs. 

 The respiratory quotients (/ e. ratio of Oo to COo) in the two 

 species at 20° C. are as follows : — 



Influence of External Conditions upon Respiration. — 



The respiratory functions of both the lungs and the skin vary 

 in different periods of the year even when the animals are 

 placed under the same degree of temperature. The amount 

 of oxygen taken in by the lungs is greatest during the breed- 

 ing season ; then it rapidly decreases during the summer. 



