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 here introduce to render more comprehensible the passage from a material body to a spiritual action, contains only an empty explanation, for the function is not essentially distinct by its nature from the organ; it is simply “the organ in activity,” it adds to the organ taken in a state of repose but one change, viz. activity, that is to say movement, and, consequently, the function of an organ is material by the same right as the organ. When a muscle contracts, this contraction, which is the proper function of the muscular fibre, consists in a condensation of the muscular protoplasm, and this condensation is a material fact. When a gland enters into activity, a certain quantity of liquid flows into the channels of the gland, and this liquid is caused by a physical and chemical modification of the cellular protoplasm; it is a melting, or a liquefaction, which likewise is material. The function of the nerve cell is to produce movement, or to preserve it, or to direct it; it is material like the cells. There is therefore nothing in all these functional phenomena which might lead us to understand how a material cause should be capable of engendering a conscious effect.

It seems that all materialists have acknowledged that here is the vulnerable point in their theory, for it is the principle of heterogeneity which they have especially combated. But their defence is