Page 297 - Third Book of Reading Lessons

296 THIRD OOK OF
For " Oxygen," see p. 283; "Fibres," p. 137 ; "Quadrupeds," p. 95 ; "Vital,'' p. 199; "Propensity," p. 13; and "Teguments," p. 35. For deriv. of"Mammi ra," see "Mammalia," p. 227.
1. REPTILES have the heart disposed in such a manner, as that, on each contraction, it sends into the lungs only a portion of the blood which it has received om the various parts of the body, and the rest of that uid returns to the several parts, without having passed through the lungs; and undergone the action of respiration.
2. From this it results, that the oxygen acts less on the blood than in the mammi ra. If the quan­ tity of respiration in the latter animals, in wh ch the whole of the blood passes through the lungs, before returning to the parts, be expressed by unity, the quantity of respiration in the reptiles must be ex­ pressed by a action of unity so much the smaller, as the portion of the blood sent to the lungs on each contraction of the heart is less.
3. As respiration communicates to the blood its heat, and to the bres their nervous irritability, so we nd that reptiles have cold blood, and that their muscular power is less, upon the whole, than that of quadrupeds, and, consequently, than that of birds. Accordingly, they do not o en perform any move­ ments but those of creeping and of swimming; and though many of them leap, and run st enough, on some occasions, their general habits are lazy, their digestion exceedingly slow, their sensations obtuse, and in cold and temperate climates, they pass almost the entire winter in a state of lethargy. Their brain, proportionally smallr, is not so ne ssary to the ex­ ercise of their animal and vital culties, as it is in the rst two classes of the animal kingdom. They continue to live and exhibit voluntary motions after
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