The most important chemical operations performed in the manufactory are three in number. The first consists in the transformation of food into protoplasm, or cell-substance; the second, in the discharge of the energy accumulated in these cells; the third, in the elimination of those substances which the cells have exhausted and rendered useless. If we make a careful comparison, by means of chemical analysis, between the composition of the substances introduced and those eliminated, we always find that the chemical energy of the latter is much reduced, from which we may know that it is food which puts everything in movement, for with nothing, nothing is made. The walls of the building are often moistened by a fluid which trickles through in drops, and is called perspiration. Physiologists have constructed most costly apparatus in order to collect the smoke of the chimney and the air which escapes from the mouths of the innumerable ventilators called pores. Every little thing was studied and conscientiously analysed, and all were surprised that these elaborate and most intricate operations of life should result finally in products so simple. We may say that our body only produces carbonic acid, urea, and a few salts. III Let us enter more fully into this subject, so that we may understand the meaning of certain phenomena accompanying fear. The materials rendered useless in the operations of our factory are easily eliminated through the skin, which thus co-operates in one of the most important functions, that of internal cleansing, which is more particularly the office of the kidneys. We have all observed that we usually perspire when the skin is red; but there are exceptional cases, as in fear, when we perspire, although we are pale and trembling. How does it happen that we have a cold perspiration, and a perspiration with a sensation of warmth in the skin? I shall here mention an experiment of Claude Bernard. Having severed a filament of the sympathetic nerves on the neck of a horse, he saw immediately afterwards, although the animal had not moved, an abundant secretion on that half of its head where the cut had been made. The mechanism producing this phenomenon is easily understood: as soon as the nerve is severed which held the blood-vessels in check, the latter dilate, blood flows more copiously to the sudoriparous glands, increasing their activity and causing an elimination of the secreted liquid.