[46] The idea of classifying human occupations, according as they bring in play the organs of the senses, the intellect or locomotion, is a wild and useless one. This division besides is made in a way altogether defective, since in the first class it is the result of the occupations which put in play the organs, whatever may be the means of execution; in the second it is the occupation itself, whatever may be the results, and in the third, it is at the same time the execution and the result. [47] We know that at a certain period of digestion the pulse rises and respiration is accelerated; we know it, I say, but we do not know the immediate causes of the phenomenon. Is it a reason, in fact, because a little chyle enters the lacteal vessels that the heart should accelerate the course of the blood in a system of vessels entirely distinct from these? Because afterwards this chyle, mixed in a small proportion with the venous blood, goes with it through the lungs, is it a reason that the motions of the lungs should be accelerated? Undoubtedly not; besides, the acceleration is not successive in these two functions, as Bichat seems to imply. The one is the necessary and immediate consequence of the other. But why does the action of the heart increase in this second period of digestion? We cannot tell; nor do we know why it diminishes in the first; for to think of explaining it by saying that the vital forces are then concentrated at the epigastric region, is a mere illusion; it is only changing the expression of the phenomenon, and clothing it in a hypothetical form. CHAPTER IX. OF THE ORIGIN AND DEVELOPMENT OF THE ORGANIC LIFE. We have just now seen that the animal life, which is inactive in the fœtus, is developed after birth: we have also followed up the particular laws of its development. On the contrary, the organic life comes into action almost as soon as the fœtus is conceived; for as soon as the least organization is apparent, the little heart will be seen protruding its blood on all sides. The heart is the first formed part, the first in action: now, as all the organic phenomena depend upon it, we may readily conceive in what way the functions of the inward life are thrown into exercise. I. _Of the mode of the organic life in the fœtus._ Nevertheless, the organic life of the fœtus, is not the same as that which the adult is destined to enjoy. Let us enquire into the reason of this difference. We have said that the organic life is the result of two great orders of functions, of those namely of assimilation and decomposition, so as to form an habitual circle of creation and destruction. Now in the fœtus this circle is singularly contracted.