But if we would have a clear idea of this augmentation and expansion, how can it be done otherwise than by considering the animal body, and each of its parts, as so many internal moulds which receive the accessory matter in the order that results from the position of all their parts? This expansion cannot be made by the addition to the surfaces alone, but, on the contrary, by an intimate susception which penetrates the mass, and thus increases the size of the parts, without changing the form, from whence it is necessary that the matter which serves for this expansion should penetrate the internal part in all its dimensions; it is also as necessary that this penetration be made in a certain order and proportion, so that no one point can receive more than another, without which some parts would expand quicker than others, and the form be entirely changed. Now what can prescribe this rule to accessory matter, and constrain it to arrive perpetually and proportionally to every point of the internal parts, except we conceive an internal mould? It therefore appears certain that the body of an animal or vegetable is an internal mould of a constant form, but where their masses may augment proportionably, by the extension of this mould in all its external and internal dimensions. That this extension also is made by the intus-susception of any accessory or foreign matter which penetrates the internal part, and becomes similar to the form and identical substance with the matter of the moulds themselves. But of what nature is this matter which the animal or vegetable assimilates with its own substance? what can be the nature of that power which gives it the activity and necessary motion to penetrate the internal mould? and if such a power does exist, must it not be similar to that by which the internal mould itself would be produced? These three questions include all that can be desired on this subject, and seem to depend on each other so much, that I am persuaded the reproduction of an animal or vegetable cannot be explained in a satisfactory manner, if a clear idea of the mode of the operation of nutrition is not obtained; we must, therefore, examine these three questions separately, in order to compare the consequences resulting therefrom.