Comte unreservedly adopts the distinction established by Bichat between the functions of organic life and those of animal life. In the first place he concludes from this, in virtue of the correlation of the dynamic to the static point of view, that distinct tissues correspond to these distinct functions. Then, he goes more deeply into the difference between the two kinds of functions. Strictly speaking, the phenomena of organic life only constitute a special order of composition and of decomposition. They come very near to chemistry, and may serve as a transition between the inorganic world and the world of life.[172] On the contrary, the phenomena of animal life (irritability, sensibility), offer no analogy with the phenomena of the inorganic world. We might almost believe, according to Comte, that the separation is established not between the chemical and biological phenomena, but between organic and animal life, the phenomena of the former reducing themselves to physico-chemical phenomena, and those of the latter presenting entirely different characteristics. Such is not, however, Comte’s thought. Undoubtedly, considered one by one, the phenomena of organic life (absorption, circulation, exhalation, etc.) are indeed physico-chemical phenomena. But what renders their biological character irreducible is that it is impossible to consider them separately: in order to understand them we must first look at them from the point of view of the whole, and appeal to the organic _consensus_, in a word, to what Claude Bernard, will call _l’idée directrice_. In the study of organic functions we shall begin by the lower extremity in the series of living beings, that is to say by the most rudimentary forms of the vegetable kingdom, for it is here that we shall grasp the phenomena in their simplest form. Then we shall follow their growing complexity. For the animal functions, on the contrary, it is expedient to begin by man, “the only being in which such an order of phenomena is ever immediately intelligible.” From this point of view man is pre-eminently the biological unity. As soon as it is a question of the characteristics of animality, we must begin with man and see how they descend by degrees, rather than start from the sponge, and look for their mode of development. Man’s animal life helps us to understand that of the sponge; but the reverse is not true.[173] Moreover, the phenomena of organic life, being the most general, are also the most fundamental. The functions of animal life are first useful for the needs of organic life, by perfecting it. It is in man alone that the vegetative life is subordinate to the life of relation: and even for that he must have reached a high degree of civilisation.[174] VI.