Animalisation is the process by which the food is _assimilated_, that is to say, converted into animal matter; and nutrition is that by which the food thus assimilated is rendered subservient to the purposes of nourishing and maintaining the animal system. EMILY. This, I am sure, must be the most interesting of all the branches of chemistry! CAROLINE. So I think; particularly as I expect that we shall hear something of the nature of respiration, and of the circulation of the blood? MRS. B. These functions undoubtedly occupy a most important place in the history of the animal economy. --But I must previously give you a very short account of the principal organs by which the various operations of the animal system are performed. These are: The _Bones_; _Muscles_, _Blood vessels_, _Lymphatic vessels_, _Glands_, and _Nerves_. The _bones_ are the most solid part of the animal frame, and in a great measure determine its form and dimensions. You recollect, I suppose, what are the ingredients which enter into their composition? CAROLINE. Yes; phosphat of lime, cemented by gelatine. MRS. B. During the earliest period of animal life, they consist almost entirely of gelatinous membrane having the form of the bones, but of a loose spongy texture, the cells or cavities of which are destined to be filled with phosphat of lime; it is the gradual acquisition of this salt which gives to the bones their subsequent hardness and durability. Infants first receive it from their mother’s milk, and afterwards derive it from all animal and from most vegetable food, especially farinaceous substances, such as wheat-flour, which contain it in sensible quantities. A portion of the phosphat, after the bones of the infant have been sufficiently expanded and solidified, is deposited in the teeth, which consist at first only of a gelatinous membrane or case, fitted for the reception of this salt; and which, after acquiring hardness within the gum, gradually protrude from it. CAROLINE. How very curious this is; and how ingeniously nature has first provided for the solidification of such bones as are immediately wanted, and afterwards for the formation of the teeth, which would not only be useless, but detrimental in infancy! MRS. B. In quadrupeds the phosphat of lime is deposited likewise in their horns, and in the hair or wool with which they are generally clothed. In birds it serves also to harden the beaks and the quills of their feathers. When animals are arrived at a state of maturity, and their bones have acquired a sufficient degree of solidity, the phosphat of lime which is taken with the food is seldom assimilated, excepting when the female nourishes her young; it is then all secreted into the milk, as a provision for the tender bones of the nursling. EMILY.