The environing containable fluids are, then, for the living body of very great simplicity, a veritable chyle entirely prepared by nature.
"Mutilation cannot operate without gradually increasing the consistence of the parts contained within the minute new organism and without extending its dimensions.

Hence soon arose the second of the vital functions, _growth or internal development_." _First Faculty of Animal Nature._--Then gradually as the continuity of this state of things within the same minute living mass in question increases the consistence of its parts enclosed within and extends its dimensions, a vital orgasm, at first very feeble, but becoming progressively more intense, is formed in these enclosed parts and renders them susceptible of _reaction_ against the slight impression of the fluids in motion which they contain, and at the same time renders them capable of contraction and of distention.

Hence the origin of _animal irritability_ and the basis of feeling, which is developed wherever a nervous fluid, susceptible of locating the effects in one of several special centres, can be formed.
"Scarcely will the living corpuscle, newly animalized, have received any increase in consistence and in dimensions of the parts contained, when, as the result of the organic movement which it enjoys, it will be subjected to successive changes and losses of its substance.
"It will then be obliged to take nourishment not only to obtain any development whatever, but also to preserve its individual existence, because it is necessary that it repair its losses under penalty of its destruction.
"But as the individual in question has not yet any special organ for nutrition, it therefore absorbs by the pores of its internal surface the substance adapted for its nourishment.

Thus the first mode of taking food in a living body so simple can be no other than by absorption or a sort of suction, which is accomplished by the pores of its outer surface.
"This is not all; up to the present time the animalized corpuscle we are considering is still only a primitive animalcule because it as yet has no special organ.

Let us see then how nature will come to furnish it with any primitive special organ, and what will be the organ that nature will form before any others, and which in the simplest animal is the only one constantly found; this is the alimentary canal, the principal organ of digestion common to all except colpodes, vibrios, proteus (amoeba), volvoces, monads, etc.
"This digestive canal is," he says--proceeding with his _a priori_ morphology--"a little different from that of this day, produced by contractions of the body, which are stronger in one part of the body than in another, until a little crease is produced on the surface of the body.