VITALISM : A HRIEK HISTORICAL AND CRITICAL REVIEW. 323 express the entire phenomenal world. It would seem indeed that the various activities manifested in heat, electricity, magnetism, etc., which various sensations differently inter- pret, are capable of being described in terms of each other ; and analogy naturally would extend this process of correlation to vital phenomena themselves. At present, however, various considerations can still be brought forward to make at least
- i temporary retention of the word " vital " desirable.
With some show of truth the vitalist may maintain that if the physicist erects an atomic structure wherein are embodied various properties of matter, he himself has the same right to endow an equally chimerical special principle with the manifold characters of life. Without doubt he has this right, as indeed the chemist may legitimately ex- tend it so as to speak of an aqueous principle in water or of a calcareous principle in chalk, if the figure of speech may be of service to him. That Natural Science does not object to the employment of the concept for descriptive purposes is sufficiently demonstrated in the case of the principle of " nascent action " which, for a long time accepted as under- lying many unusual chemical actions, has at length been replaced by an extension of mechanical terminology. Physiologists have often availed themselves of this licence. Following the custom of physicists in their use of the term "force" as a convenient mathematical abstraction, they attribute to certain phenomena vital force, vital energy or vital action, where physical and chemical forces, energies or actions are as yet inadequately discovered (22). In this sense all varieties of so-called automatic activity have been ascribed to the energy of the vital principle. Similarly, certain observers have distinguished physiological (i.e. vital) from physical osmotic action within the intestine. Other observers, again, have insisted on the vital nature of the process of gaseous change within the lungs. And there are many further examples. But throughout, this usage of the term " vital " merely implies that the phenomena in question are each the expression of an appropriate system of forces which, even if it be nothing more than a complex composi- tion of ordinary mechanical forces, yet represents activities apparently so different from lifeless movements that it seems at present desirable to reserve for the force some special epithet. On the other hand, there have not been wanting those who are ready to exceed this privilege. Vainly confident that the mere invocation of a special force or principle can explain the obscurest of natural phenomena, many physiolo-
