20 SEALS OF THE SHETLAND ISLANDS. 



Such a change might be effected, for instance, by the liver, 

 which in seals, as in fish, is of great size, or by the kidneys 

 and intestines, but perhaps equally by the skin, for, re- 

 maining so long under water, and even when above it per- 

 forming so few respirations, it seems clear that much car- 

 bon, which in land animals is discharged by the lungs, 

 must, in aquatics, be emitted through other channels. Of 

 this view, the strong carburetted odour of the skin of the 

 P. barbata may be considered as a not very obscure indica- 

 tion. The dark colour of the blood, it is true, is one of its 

 venous characters, but I suspect we are hardly yet so ac- 

 quainted with its chemical and vital nature, as to deny that 

 some of its qualities may be modified, and yet this colour re- 

 main. But, even supposing that the venous blood of diving 

 animals is the same in quality as ours, and that it circu- 

 lates, in like manner, through the cerebral arteries, where 

 is the certainty of the position, that this must, in the same 

 time, produce death in them as in us ? We have as little 

 reason to assume that the venous influence on them is the 

 same in kind and degree as it is on us, as that opium or al- 

 cohol should have a similar effect on both. Can organiza- 

 tion give a reason why one plant is wholesome food to a 

 goat and deadly poison to a sheep ? — why one animal 

 should remain torpid for months and then revive, while a 

 congenerous one never can assume this state? — why one 

 species of bird can remain only two minutes under water 

 and another eight, the seal twenty, and the whale one hun- 

 dred ? — why pearl-divers can, from habit, remain so much 

 longer under water than other men ? Of all these modifi- 

 cations of the vital principle, structure can afford us no so- 

 lution ; and these remarks may tend to shew, that, in the 

 quality of the blood or susceptibility of the nervous system, 

 at least as plausible a theory may be looked for as in pecu- 

 liarity of organization, which has, on this point, so long 



