although, from the greater sensibility of their organs, they are rather sooner affected by those causes than other animals.

The importance of different degrees of sensibility to animals of different size, and the indispensable necessity that each animal should have its appropriate degree to accomplish its suitable relation with the laws of the physical world, must now be sufficiently apparent. Whether this degree of sensibility be determined by the force and frequency of the pulsatory circulation, or whether the force and frequency of the pulsatory circulation, be an effect of the electrical operations by which sensibility is accomplished, may be a subject of some doubt; but, in either case, the force and frequency of arterial action are always correspondent with the degree of sensibility, so that they may at all times be considered the indication, if not the cause, of the degree of sensibility. Hence, we may understand why any unnatural increase or diminution of arterial action is accompanied by a destruction of that just relation, between the perceiving power of the animal and the laws of the material world, on which life and health are dependent. Where an unnatural increase of pulsatory circulation

occurs, the sensibility not only becomes increased, but the very action of the pulsating artery is conveyed by sensation, to the perceiving power, and constitutes the throbbing of inflammation. The irregular supplies of food to the greater part of the animal creation, but more particularly to that which is dependent upon prey, must occasion great variations in the quantity of circulating fluid; yet this is not attended by any material change in the sensibility of the animal, because there is made up in frequency of circulation, what is lost in fulness of pulse: hence the pulse of the starving man is always extremely small and quick, and nothing but food will check its action. Persons suffering under diseases of exhaustion, have also this small and quick pulse. Bleeding, in health, invariably increases the quickness of pulse, but it is not perceivable until the natural degree of sensibility is restored; which, during the operation, is generally much diminished. It must also be evident, from the foregoing reasoning, that the infant, partaking of the nature of the smaller animals, has occasion for a greater degree of sensibility than the adult; this is accompanied by a more rapid circulation, and thence the frequency of the infantile pulse, and not as has been represented

by M. Bichat, from any superabundance of life. Hence, also, it is, that the circulation in small men is more active than in large; and the pulse of woman, from her smaller size, is generally quicker than of man. If this frequency of pulse in the infant were, as M. Bichat has represented, from a superabundance of life, a reduction of it might be safely effected; but if the experiment be made by reducing it to the frequency of an adult pulse, the infant's sensibility will be so much reduced, as to destroy totally its connection with the laws of the material world; or, in other words, it will cease to live. On the contrary, if we attempt to force the circulation of large animals to the frequency of the smaller, we so completely alter their sensibility, as to unfit them for a proper estimation of the force of the natural causes to which they have been accustomed; and hence, they neither feel nor act in their usual manner, but present those states known as drunkenness, delirium, or madness.

There is a simplicity, beauty, and importance, in all the known laws of Nature, so far as they have been ascertained by philosophy, which would lead us to expect the same in the economy and structure of animals. But, in the

present received notions of life, there is found an useless complexity and a series of encumbering operations, quite at variance with the nice adaptation of means to an end, and by which, according to present received notions, the animal is continually endangered, without any adequate utility. In treating of these operations in connection with this subject, the path to which is now rendered easy and pleasant, it will appear, that where mankind have taken up notions at variance with great simplicity and nicety of design, such notions are without rational support, and are opposed by almost every circumstance connected with the opinion, as will appear as we proceed.

Several of the following chapters, although the Disquisition be conducted under different heads, have an intimate connection with the present subject-Sensibility; and proofs of the proposition advanced in this chapter, will be continued through those which follow.

CHAPTER IV.

Assimilating organs-the uses of food-taking— decomposition of the body questioned-The preservative principle of flesh, or Mr. Hunter's vital principle-may be exhausted-and again restoredWhat this principle is—Whence derived-Facts in support-On the required quantities of food-Conclusion.

THERE is in every living creature an extensive and important series of operations, of which a lengthened description and detailed consideration will be here unnecessary. In these operations, a considerable portion of animal structure, comprising a large assemblage of organs, is employed; and they consequently become a matter of inquiry in connection with the present subject. These operations, comprising digestion, nutrition, and their concomitant functions, when regarded collectively, are usually called the functions of assimilation; which terms, although they do not exactly meet my views of the ultimate uses of those operations, may be retained for the present. It is sufficiently reasonable to admit, that the functions of assimilation may be for the purpose