It is not surprising, therefore, that we are more subjected than animals to infirmities; since we know not so well as them, what may contribute to preserve or destroy health, our experience being less certain than their perception; nay we abuse the very senses of the appetite, which they enjoy in such superior excellence, these being to them the means of preserving health, and to us causes of disease and of destruction. By intemperance alone more men sicken and die, than by all the scourges incident to human nature.
From these reflections it would appear, that animals have a more certain, as well as a more exquisite sensation of feeling than men. In support of this superior strength of sentiment, we may advert to their sense of smelling, which some animals enjoy to such a degree that they can smell further than they can see. A sense like this is an eye which sees objects, not only where they are, but even where they have been; it is the sense by which the brute animal distinguishes what is suitable or repugnant to its nature, and by which it perceives and chooses what is proper for the gratification of its appetite.
In greater perfection, then, than man, do animals enjoy the senses which relate to appetite: and though of their present existence they have a consciousness, of their past they have none. This second proposition, as well as the first, is worthy consideration. The consciousness of existence is composed in man of the sensation of his present, and of the remembrance of his past existence. Remembrance is a sensation altogether as present as the first impression, and sometimes affects us more strongly. As these two kinds of sensations are different, and as the mind possesses the faculty of comparing and forming ideas from them, our consciousness of existence is the more certain and extensive, as remembrance more frequently and copiously recalls past things and occurrences; and as by our reflections we compare and combine them with those past and present occurrences. Every man retains within himself a certain number of sensations correspondent with the different existences or states through which he has passed; and these sensations, by the comparison which the mind forms between them, at length become a succession, and a series of ideas. In this comparison of sensations consists the idea of time; and indeed all other ideas. But this series of ideas, this chain of existences, is often presented to us in an order very different from that in which our sensations reached us; and in this it is that the difference principally consists in the genius and disposition of mankind.