[50] When two phenomena are seen to follow each other immediately, we are naturally led to consider one as the cause of the other. _Post hoc ergo propter hoc._ It is a form of reasoning which is very often abused. Food taken into the mouth touches the orifice of the salivary ducts, the fluid flows out, and it is then concluded that the salivary gland has been excited by the impression made on the extremity of its canal. At the moment of birth, the orifice of the urethra is exposed to the contact of the air, and soon the kidneys begin to secrete; then it is the impression of the air on the urethra that has produced their action. But is not this contact of the food in the one case, and of the air in the other an accidental and purely accessory circumstance? Do we believe, that if by any cause the opening of the prepuce was entirely obliterated, the secretion of urine would be prevented? Do we not know that if instead of taking into the mouth savoury food, it is brought near to it, the saliva flows not less, or in vulgar language the mouth waters? There is however no contact, there is not any mechanical or chemical impression in the orifice of the salivary ducts. CHAPTER X. OF THE NATURAL TERMINATION OF THE TWO LIVES. We have just now seen, that the two lives commence at distant epochs; we have seen them developing themselves according to laws, which are exactly the reverse of each other. I shall now attempt to describe them, as they terminate; and this they do in a very different manner also, assuming characters at such time as distinct and separate, as those which they possess during the periods of their activity. In this place, I shall speak of natural death only; those deaths, which originate in accidental causes, will be the object of the second part of this work. I. _In Natural Death the animal life is the first to cease._ Natural death is remarkable for the following reason chiefly:--it terminates the animal life, a long time before it puts an end to the organic life. He who dies in consequence of a very prolonged old age, dies in detail; his exterior functions are finished, one after the other; the senses are shut up successively; the ordinary causes of sensation pass over them, and do not affect them. The sight grows dull and confused; it ceases at length to transmit the images of objects: this is the blindness of old age; sounds also, after a certain time, affect the ear confusedly; the organ at last becomes entirely insensible. The cutaneous covering of the body grows hard and dry; it is the seat of an obscure and imperfect touch. Besides which, the habitude of feeling has blunted the power of feeling; at the same time all the other organs which are dependent on the skin, grow weak and perish; the hair falls, it is deprived of the juices by which it was nourished: to continue our description, odours make but a feeble impression upon the nostrils.