243. This result is referable to the principle already shown to be characteristic of living substance,—namely, the power of resisting, within a certain range, the ordinary influence of physical agents. The operation of this power is illustrated in a beautiful manner in a series of experiments performed by Mr. Hunter on the egg and on blood. This physiologist exposed a live, that is, a fresh egg to the temperature of the 17th and the 15th degrees of Fahrenheit; it took half an hour to freeze it. The egg was then thawed and exposed to 10° less cold, namely, to the 25th degree of Fahrenheit; it was now frozen in a quarter of an hour. A living egg and one that had been killed by having been first frozen and then thawed, were put together into a freezing mixture at 15°: the dead was frozen twenty-five minutes sooner than the living egg. The undiminished vitality of the fresh egg enabled it to resist the low temperature for the space of twenty-five minutes; the vitality of the frozen egg having been destroyed, it yielded at once to the influence of the physical agent. On subjecting blood to analogous experiments, the result was found to be the same. Blood immediately taken from the living vessel, and blood previously frozen and then thawed, being exposed to a freezing mixture, a much shorter period and a much less degree of cold were required to freeze the latter than the former. 244. ii. The vitality of the blood is proved by the change it undergoes in becoming a constituent part of an organized tissue. The blood conveys to the several tissues the constituents of which they are composed; each tissue selects from the mass of blood its own constituents and converts them into its own substance, in which conversion, since the blood always goes to the tissue in a fluid form, the blood must necessarily pass from a fluid into a solid. In the vessels the vital endowment of the blood maintains it permanently fluid; in the structures the same power makes it and keeps it solid. One and the same substance in one and the same body, in one part is always fluid, in another always solid; the fluid is every moment passing into the solid and the solid into the fluid, without intermixture and without interference. Nothing analogous to this is ever witnessed in inorganic matter, in physical mechanism; it is peculiar to the organized body and distinctive of the mechanism of life. Sometimes in physical mechanism we can perceive the mechanical arrangements and distinctly trace them from beginning to end: in vital mechanism, even when we can discern the mechanical arrangements, we can seldom trace them beyond a step or two, and never from beginning to end; but arrangement and adaptation we know there must be in that which goes beyond, no less than in that which keeps within, our perception, and we ought scarcely to question the existence of adjustments, because they elude our sense, when probably the very reason why they do so is