INTRODUCTORY OBSERVATIONS. 77 



carbonic acid when in contact with the atmosphere ; but the 

 subject had never undergone that strict and philosophical in- 

 vestigation by which all its important bearings should be 

 ascertained, until Dr. William Edwards of Paris entered 

 upon the inquiry, the results of which he published in his 

 admirable work " On the Influence of Physical Agents on 

 Life ;" than which there does not exist in the whole range of 

 physiological literature a more perfect example of the manner 

 in which a physiological inquiry ought to be imagined, planned, 

 and conducted, and its results reasoned upon, and described. 

 As I have endeavoured in the article already quoted, to give a 

 short sketch of the principal results of Dr. Edwards^s expe- 

 riments, I shall now merely offer a somewhat modified quo- 

 tation from that article, rather than enter at length into the 

 detail, which, however interesting the subject may be to the 

 physiologist, would be out of place in the present work, and 

 would be unnecessary to those who alone could appreciate it; 

 for where is the physiologist who has not read and admired 

 the original work itself ? 



The existence of cutaneous respiration in the Frog was 

 proved by the simple experiment of tying a piece of bladder 

 over the head so tightly as to prevent the possibility of com- 

 munication with the lungs, so as indeed to produce complete 

 strangulation. The Frogs were then placed under water ; 

 and on examining the air contained in the vessel after an hour 

 or two, a sensible quantity of carbonic acid was detected. 



On placing Frogs in vessels filled respectively with river 

 water, and with water which had been deprived of air by 

 boiling, and inverted over the apertures contained in the 

 shelf of a pneumatic trough, containing about ninety-eight 

 pints, those in the latter lived on the average little more than 

 half as long as those in the aerated water. On trying the 

 effects of submersion under stagnant water frequently re- 

 newed they lived two months and a half, and then died from 



