==The Living Body is a Machine.==--Reviewing the subject up to this point, what must be our verdict as to our ability to understand the running of the living machine? In the first place, we are justified in regarding the body as a machine, since, so far as concerns its relations to energy, it is simply a piece of mechanism--complicated, indeed, beyond any other machine, but still a machine for changing one kind of energy into another. It receives the energy in the form of chemical composition and converts it into heat, motion, nervous wave motion, etc. All of this is sure enough. Whether other forms of nervous and mental activity can be placed under the same category, or whether these must be regarded as belonging to a realm by themselves and outside of the scope of energy in the physical sense, can not perhaps be yet definitely decided. We can simply say that as yet no one has been able even to conceive how thought can be commensurate with physical energy. The utter unlikeness of thought and wave motion of any kind leads us at present to feel that on the side of mentality the comparison of the body with a machine fails of being complete. In regard to the second half of the question, whether natural forces are adequate to explain the running of the machine, we have again been able to reach a satisfactory positive answer. Digestion, assimilation, circulation, respiration, excretion, the principal categories of physiological action, and at least certain phases of the action of the nervous system are readily understood as controlled by the action of chemical and physical forces. In the accomplishment of these actions there is no need for the supposition of any force other than those which are at our command in the scientific laboratory.