But with all this the achievements of the protoplasm remained unaccountable: it seemed forbidden to life that it should understand itself. Most of the biochemical processes were not only unknown, it lay in their very nature that they should escape attention. Almost nothing was known of the structure or composition of the living unit called the “cell.” What use was there in establishing the components of lifeless muscle, when the living did not let itself be chemically examined? The changes that took place when the rigor mortis set in were enough to make worthless all investigation. Nobody understood metabolism, nobody understood the true inwardness of the functioning of the nervous system. To what properties did the taste corpuscles owe their reaction? In what consisted the various kinds of excitation of certain sensory nerves by odour-possessing substances? In what, indeed, the property of smell itself? The specific odours of man and beast consisted in the vaporization of certain unknown substances. The composition of the secretion called sweat was little understood. The glands that secreted it produced aromata which among mammals undoubtedly played an important role, but whose significance for the human species we were not in a position to explain.