des Agcns Physiques sur la Vie, 149 



?iir entered in combination with water was shewn from Dr. 

 Edwards nei^er having seen water in the lungs^ Therefore, 

 unless the air acted on the blood through some other organ, 

 the lives of these animals would be definite and shortened, 

 even though the water be renewed from time to time, and 

 their asphyxy would be complete and continued. And since 

 the skin is the only organ in contact with the air, it ig fair to 

 conclude that it is the medium of atrial absorption. 



When the webs: were examined under water, these mem- 

 branes indicated the action of air upon their blood-vessels, by 

 the bright tint of the blood. . i'^ujv/ i-)U\ii. ^iiiol oa boni.-a > . 

 Spallanzani imagined that frogs petish BOOTierm running 

 than in stagnant water ; but Dr. Edwards having secured 

 some of these animals in ten feet of the Seine, whilst others 

 were simultaneously placed in unrenewed stagnant water ^ he 

 found the latter did not survive many hours, and the former 

 lived a long time. 



In order to fix the limits of this kind of existence, frogs 

 were placed in renewed aUrated water, and with a tempera- 

 ture never forced beyond ten degrees they were found to 

 live in all seasons of the year ; but when the temperature 

 was elevated from twelve to fourteen, they died in a few 

 hours. In running streams they lived longest, and at twelve 

 degrees they were thus more favourably placed than in stag- 

 nant water, at a lower temperature even, and taking the pre- 

 caution to renew the water daily ; and at seventeen degrees 

 in running water they died prematurely. Toads exhibited 

 the same comparative results, but they lived the longest. 



It appears, therefore, that water contained in vessels is less 

 favourable to the lives of these animals than running streams, 

 although the water and the temperature were identical. 

 Probably the great advantage of running water is its con- 

 stant and unceasing renewal. The separate and comparative 

 influence of air, water, and temperature, being thus investi- 

 gated, the combined action of the three physical agents was 

 next inquired into, and it is demonstrated that frogs sub- 

 mersed in water are influenced by three circumstances, — !• 

 the presence of air in water ; 2. the quantity of its renewal ; 

 3. the temperature of the medium. If the manners of frogs 

 be closely examined, they appear to live in water under very 

 considerable influence from the atmosphere. 

 ■ From circumstances developed in the foregoing experi- 

 ments, cutaneous respiration seems to be pretty evidently in- 

 dicated. A chapter is, therefore, devoted to this subject, one 

 that is not well known, although pulmonary respiration ia 



