76 



HARDWICKE'S SCIENCE-GOSSIP. 



the oesophagus being closed to prevent its passing 

 into the stomach ; then the posterior opening of the 

 nostrils being also closed by the application of the 

 tongue the pharynx is contracted and the air forced 

 into the lungs. 



The lungs are of considerable size, lying on each 

 side of the vertebral column ; they consist of large 

 cells separated by the most beautifully delicate 

 diaphanous parietes. From this peculiarity in the 

 respiration, it follows that it can only be performed 

 when the mouth is closed ; and that if the mouth be 

 gagged open the animal would soon perish from the 

 cessation of pulmonary respiration. The respiration 

 of the toad is, as I said before, cutaneous as well as 

 pulmonary ; this cutaneous respiration of the toad 

 is the power, possessed not only by the toad but 

 indeed by the batrachians generally, which the 

 surface of the skin possesses of effecting those 



aerated water. On trying the effects of submersion 

 under stagnant water frequently renewed they lived 

 two months and a half, and then died from accidental 

 neglect of changing the water. 



The results of placing them under running water 

 were similar. In this case they were confined in a 

 sort of cage and sunk in the river. 



Such is a slight glance at the results obtained with 

 reference to the cutaneous respiration carried on 

 through the medium of aerated water ; and those 

 connected with the atmospheric respiration of the 

 same surface are no less conclusive. Another experi- 

 ment was performed by the total excision of the 

 lungs, and of three frogs thus treated two died on 

 the thirty-third and one on the fortieth day. The 

 toads, too, have been kept alive for months in nets 

 sunk under running water at a low temperature 

 without any direct access to atmospheric air. 



Fig. 48. — Common Toad (Bufo vulgaris). 



changes in the blood which are usually performed 

 by the lungs or branchiae. Dr. William Edwards, 

 of Paris, entered upon the inquiry into this subject. 

 I regret that he made his experiments on frogs in- 

 stead of toads, but as both animals possess the power 

 of cutaneous respiration, and are closely related, the 

 results would most probably be much the same. 

 The existence of cutaneous respiration in the frog 

 (whose relation to the toad is very close) was proved 

 by the simple experiment of tying a piece of bladder 

 over the head so tightly as to prevent the possibility 

 of communication 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 sen- 

 sible 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 con- 

 tained 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 



Fig. 49. — Natterjack Toad (Bufo calamita). 



The results of other experiments have proved that 

 pulmonary respiration alone is not sufficient to 

 support life without the aid of that of the cutaneous 

 surface. 



It is very clear that this important function cannot 

 be carried on unless the surface be constantly kept 

 in a moist state. The branchiae of fishes and of 

 Crustacea and the lungs of all pulmoniferous animals 

 equally require that the respiratory surface in every 

 modification should be humid ; for as soon as it 

 becomes dry its function ceases and the animal 

 speedily dies. But as the toad is frequently exposed 

 to a dry atmosphere it is essential that there should 

 be some provision made for a constant supply of 

 moisture to the skin, which has just been shown to 

 be a respiratory surface. 



This is effected precisely as in other surfaces which 

 perform this function, namely, by a secretion of fluid 

 from the surface itself. The extent of the skin is, 

 however, so great that the whole internal moisture 

 of the animal would speedily be exhausted unless 

 a reservoir were provided for an extraordinary de- 



