Accordingly it would seem possible to construct a table of all the possible forms of energy by assigning to the factors of energy all possible manifoldness characteristics and combining them in pairs, with the subsequent elimination of the products which do not conform to the conditions stated on p. 234. By comparison with all the forms of energy known at the time, it would be possible to discover the forms that were still unknown and to outline their most important properties. Experience would merely have to discover their specific constants. For some years I have myself from time to time attempted to carry out this program; but hitherto I have not progressed far enough to justify the publication of the results already obtained.
If now we turn to the biological sciences, the new phenomenon we meet is life. If we limit ourselves to observable facts excluding all hypotheses, we shall recognize as the universal characteristic of all life-phenomena the stationary stream of energy which flows through a comparatively constant structure. Metabolism is merely a part, though a most important part, of this stream. Plants, particularly, demonstrate immediately the paramount importance of energy in its most immaterial form, the sunbeams. Self-maintenance and repair with the production of similar descendants are other essential characteristics. All these characteristics must be present in order that an organism may arise. Furthermore they must be present if the knowing individual is to be capable of forming, by repeated experiences, a concept of any given organism, say a lion or a mold. Other organisms not fulfilling these conditions may occur. Because they are unique, they do not lead to the concept of a species, but are excluded (except of course for special purposes) from scientific consideration as 'malformations' or 'monsters.'
Whereas organisms mostly deal with forms of energy which are familiar to us in the inorganic world, we find the higher forms possessed of organs which undoubtedly produce, or are active in, the transformation of energy, though we do not know which form of energy acts within them. These organs are termed nerves; and their functioning is regularly of such a nature that upon the application of a definite form of energy to one end, they call into action at the other end forms of energy there present and which there act in their own peculiarly characteristic way. That energetic changes do occur in the process of nerve-transmission may be regarded as settled. We are therefore justified in speaking of nerve energy, leaving the question open as to whether it be a special form of energy or merely chemical energy or lastly a combination of several forms of energy.
While these processes of nerve stimulation with corresponding reaction in the end-organ, a muscle, for example, may be observed objectively, we find within ourselves connected with this nervous process
