On the Tcviperature nj' Fmhcs. 329 



Still, however, reflecting on the great proportional size of the 

 branchial nerves, and guided by analogy, it is difficult to resist 

 the conclusion, that they are not principally concerned in the 

 performance of the function in question, and that these nerves, 

 as means, are so very ample on account of the element inhabited, 

 and the proportionally greater energy of function required to 

 produce the same effect of elevation of temperature in water and 

 in the atmosphere. On any other view, it seems difficult to ac- 

 count for the branchial nerves of these fish being proportionally 

 verv much larger than the pulmonary nerves of tiie mammalia, 

 and vastly larger than those of birds, of all animals the warm- 



est. 



"Whether there is any immediate relation between the ganglia 

 on the branchial nerves and the generation of heat in these fishes, 

 is uncei-tain, and must necessarily remain so, as long as there is 

 any doubt concerning the use of ganglia. The absence of gan- 

 glia on the principal nerves of the lungs of man, f and I believe 



• The size of the pulmonary nerves of birds, and indeed of their respi- 

 ralorv nerves generally, so far as my observations have extended, is so small 

 as lobe truly astonishing, compared with their very high temperature. And, 

 on the hypothesis of nervovis influence being essential to the production of 

 animal heat, through the agency of respiration, the necessary inference seems 

 to be, that birds require less of this influence than any other description of 

 warm-blooded animals, owing to their peculiarities of structure, both in rela- 

 tion to the diffused aerial means they possess of generating heat, and their 

 peculiar means, in their covering of feathers, of preserving it ; and, owing pro- 

 bably farther to their less expenditure of it, from the peculiarities of some 

 of their principal secretions, especially those of the kidneys, skin, and lungs ; 

 their kidneys secreting an almost solid urine; their skin exhaling little mois- 

 ture, and that not in sweat, but entirely by insensible perspiration ; and their 

 lungs, though exhaling more, from the nature of the function they perform, 

 yet less than might at first be supposed, part of the aqueous vapour contained 

 in the air expired being, I believe, condensed before it enters the atmosphere 

 by the trachea, mouth, and beak, especially the latter, which are always com- 

 paratively cool. And, in accordance with this view, from the experiments of 

 Messrs Allen and Pepys, it appears even, in one instance at least, that one of 

 the warmest of birds, the pigeon, consumes, in relation to its bulk, less oxygen, 

 or produces less carbonic acid, than a quadruped, the Guinea pig, the tem- 

 perature of which is several degrees lower. 



t Haller, speaking of the great sympathetic nerve, which in man is so 

 amply provided with ganglia, says, " In pectore notabiles ramos paucos edit. 

 Neque memini me alicujus monienti truncos vidisse qui ad nervum octavi 

 paris accederent ; etsi ejusmodi nervi illustribus viris visi sunt" — Element. 



