AMPHIBIA. 



103 



process I have repeatedly watched. I have 

 observed shreds of cuticle hanging about the 

 terrestrial salamander, which would lead to the 

 opinion that this animal does not disengage 

 itself from its deciduous skin in the same 

 manner as the toad ; but as the individuals 

 under notice were not in health, the observa- 

 tion is inconclusive. 



But the most interesting circumstance con- 

 nected with the functions of the integuments of 

 these animals, or indeed with any part of their 

 economy, is their cutaneous respiration, or the 

 power which the dermal surface possesses of 

 effecting those changes in the blood, which are 

 essential to life, and which are usually per- 

 formed by particular organs set apart for that 

 express object, and modified according to the 

 aquatic or atmospheric medium in which the 

 depurating agent is applied to them. 



Although the experiments of Spallanzani had 

 long ago demonstrated that carbonic acid was 

 produced by the contact of the atmosphere 

 with the skin of frogs, the subject had never 

 been examined with the care and attention 

 which its importance demands, until the in- 

 vestigations of Dr. Edwards of Paris, given in 

 his work " On the Influence of Physical Agents 

 on Life," set the question at rest, and esta- 

 blished the proposition by a series of interesting 

 experiments, so admirably arranged, so satis- 

 factorily conducted, and so logically reasoned 

 upon, as to leave no vacuity in the regular 

 line of induction, nor doubt of the strict correct- 

 ness of his conclusions. 



The existence of a cutaneous respiration in 

 frogs was proved by the simple experiment of 

 tying a piece of bladder over the head so tightly 

 as to produce complete strangulation, and then 

 placing them under water. On examining the 

 air contained in the vessel after an hour or two, 

 a sensible quantity of carbonic acid was de- 

 tected. 



On placing frogs in vessels filled respec- 

 tively with river water and with water which 

 had been deprived of its air by boiling, and 

 inverted over the apertures perforated in the 

 shelf of a pneumatic trough, containing ninety- 

 eight and a half pints, those in the latter lived 

 on the average little more than half as long as 

 those in the aerated water. On trying the 

 effect of stagnant water renewed at intervals, 

 they were found to live two months and a half, 

 and then died from accidental neglect of renew- 

 ing the water. Similar results followed ex- 

 periments made under running water. The 

 effects of temperature in these experiments 

 were very striking, and prove that the duration 

 of life under water is in an inverse proportion 

 to the elevation of the temperature from 32 to 

 about 107, at which point the animals die 

 almost instantly. But these effects of tempera- 

 ture were found to be modified by an increase 

 of respiration, whether by their rising to the 

 surface and breathing the atmosphere, or by 

 the quantity of aerated water being increased. 



Such is a rapid glance at some of the results 

 observed by this distinguished physiologist, on 

 the cutaneous respiration of aerated water ; 



those which are connected with atmospheric 

 respiration by the same surface are no less 

 interesting. In order to render the experiments 

 as rigorously satisfactory as possible, pulmo- 

 nary respiration was prevented by actual stran- 

 gulation, rather than by keeping the mouth 

 open, a method which appears liable to some 

 degree of uncertainty. A ligature was passed 

 round the neck of six frogs, using the most 

 rigid compression, so as completely to exclude 

 any possible passage of air. One of them 

 lived twenty days ; those placed in five ounces 

 and a half of water had died in from one to 

 three days. As the severity of the operation 

 of strangulation might probably have hastened 

 death, another mode was tried, namely, the 

 total excision of the lungs, an operation which 

 appeared to produce but little suffering; the 

 animals were then placed on moist sand. Of 

 three frogs thus treated, two died on the thirty- 

 third day, and the remaining one on the 

 fortieth. 



Other experiments were instituted to resolve 

 the converse of the former proposition, whether 

 life can be prolonged by pulmonary respiration 

 alone, unaided by that of the skin ? The re- 

 sult of the experiments made upon tree frogs 

 and upon the bitfu obstetricans, was that pul- 

 monary respiration is not sufficient to support 

 life, without being accompanied by the influ- 

 ence of the skin. 



The results of these experiments are not 

 only highly interesting as regards the habits of 

 the particular tribe of animals which were the 

 subject of them, but still more so with refer- 

 ence to some important questions in general 

 physiology ; but as their bearing on these 

 points can only be shown by viewing them in 

 relation with all the other subjects treated of in 

 the admirable work from which they are taken, 

 it would be out of place to consider them here. 

 It is impossible, however, not to be struck 

 with the evidence they afford, that the respi- 

 ratory organ, that surface through the medium 

 of which the blood undergoes its necessary 

 change by the action of oxygen, whether pul- 

 monary, branchial, or cutaneous, and whether 

 the medium of its access be water or the at- 

 mosphere, is in all cases similar, being a 

 modification of the cutaneous surface. And 

 as we see in the instance before us, the same 

 surface capable of performing either atmos- 

 pheric or aquatic respiration, the inference is 

 obvious, that pulmonary and branchial organs 

 may, and probably do, possess an identity of 

 structure.When it is considered too that moisture 

 is absolutely essential to atmospheric respira- 

 tion, whether pulmonary or cutaneous, the 

 identity of the two processes becomes still 

 more unequivocal. 



This view of the subject receives considerable 

 confirmation from the fact that branchiae are 

 in many animals capable of exercising the 

 office of atmospheric respiration through the 

 medium of a very small quantity of water ; as 

 the land crabs of torrid regions are enabled to 

 traverse immense districts under a burning 

 sun, by means of those little reservoirs of 



