Is the counteracting agent which modifies this result, and prevents the injurious effects, which, under exposure to great external heat, would ensure certain destruction. And this too, it will have been seen, is provided at the expense of the animal food. When from excessive heat, caused by violent exercise or otherwise, by which respiration is accelerated and the animal temperature becomes elevated, the papillæ of the skin pour the limpid fluid through their innumerable ducts, which in its conversion into vapor, seize upon the animal heat and remove it from the system, producing that delicious coolness so grateful to the laboring man and beast in a sultry summer's day. These two opposing principles, like the antagonistic operations of the regulator in mechanics, keep up a perfect balance in the vital machine, and enable that entire division of the animal creation, distinguished as warm-blooded, including man and the brute, all the feathered tribes, the whale, the seal, the walrus, &c., to maintain an equilibrium of temperature, whether under the equator or the poles; on the peaks of Chimborazo, the burning sands of Zahara, or plunged in the depths of the Arctic Ocean. The connection between the size of the lungs, and the aptitude of animals to fatten, will be more apparent from the fact, that the carbon and hydrogen which are abstracted, constitute two of the only three elements of fat. The larger size, the fuller play, and the greater activity of the lungs, by exhausting more of the materials of fat, must necessarily diminish its formation in the animal system; unless it can be shown, which has never yet been done, that the removal of a portion of the fat-forming principles accelerates the assimilation of the remainder. The Food which supplies Respiration. This, in the herbivorous animals, after they are deprived of the milk, which furnishes it in abundance, is the starch, gum, sugar, vegetable fats, and oils that exist in the vegetables, grain, and roots which they consume; and in certain cases where there is a deficiency of other food, it is sparingly furnished in woody and cellular fibre. All these substances constitute the principal part of dry vegetable food, and are made up of three elements, _which in starch, gum, cane-sugar, and cellular fibre, exist in precisely the same proportions_, viz: 44 per cent. of carbon, 6.2 of hydrogen, and 40.8 of oxygen.