150 . Dr. Edwards, De V Influence 



generally understood. In frogs, the function of pulmonary 

 respiration is united with that of deglutition, and the air 

 enters only by the nostrils, the mouth being closed during 

 respiration. While the mouth remains open, the action of 

 deglutition is stopped, and, therefore, the animal does not 

 then breathe. Dr. Edwards availed himself of this circum- 

 stance by gagging the mouth so as to keep it open, and thus 

 prevent the air from entering the lungs. The frogs were 

 sufficiently exposed to moisture and renewal of air to their 

 bodies : the results were, that, at twenty-four degrees, five 

 frogs so placed died next day, and one lived a week. 



Dr. Edwards immersed some frogs in wet sand, and adopted 

 an improved method of excluding air from the lungs, and 

 some of them lived twenty days. Hence it evidently appears 

 that air influences the skin materially, and counterbalances 

 the asphyxious state induced by obstructing the air's passage 

 to the lungs. By adopting other methods, the existence of 

 frogs was prolonged to thirty or forty days. It is, therefore, 

 sufficiently proved that the blood undergoes its necessary 

 changes from atmospheric influence through the medium of 

 the skin, although in a minor degree compared with those 

 which it passes through from pulmonary respiration. Frogs 

 are thus shewn to possess a double source of respiration. 

 . By substituting oil for water, frogs immersed in this fluid 

 died in a few hours, being at liberty to breath the air on its 

 surface. And, when plunged into oil, with the means of 

 breathing by the lungs arrested, they lived an equal time 

 with frogs simultaneously placed in water without power to 

 respire. A comparison was instituted with frogs in oil and 

 in water, being allowed to breathe air, when the differ- 

 ence was found to be very considerable in favour of the 

 aquatic bath. These circumstances shew, that, even with 

 the feeble succour of the air through the skin, absorbed from 

 the water, the respiratory function was far more prolonged, 

 than in the case of the obstruction afforded by the oil. Thus 

 we have abundant evidence of the double function by which 

 frogs are maintained, from the action of the air on the skin 

 and the lungs ; and this appears to be the means of existence 

 among amjihibious animals generally. 



It may be asked why these animals die in deep water when 

 prevented from approaching the surface? It appears that, 

 having expelled the respired air from their lungs, which is 

 imperfectly renewed from the water, they become specifically 

 heavier than the water, and unable to rise from the bottom ; 

 and thus placed, the duration of their lives depends upon 



