The first question which presents itself is whether the only power the body possesses is, as in the case with other machines, to transform energy without being able to create or destroy it?  Can every bit of energy shown by the living organism be accounted for by energy furnished in the food, and conversely can all the energy furnished in the food be found manifested in the living organism?

The theoretical answer to this question in terms of the law of the conservation of energy is clear enough, but it is by no means so easy to answer it by experimental data.  To obtain experimental demonstration it would be necessary to make an accurate determination of the amount of energy an individual receives during a given period, and at the same time a similar measurement of the amount of energy liberated in his body either as motion or heat.  If the body is a machine, these two should exactly balance, and if they do not balance it would indicate that the living organism either creates or destroys energy, and is therefore not a machine.  Such experiments are exceedingly difficult.  They must be performed usually upon man rather than other animals, and it is necessary to inclose an individual in an absolutely sealed space with arrangements for furnishing him with air and food in measured quantity, and with appliances for measuring accurately the work he does and the heat given off from his body.  In addition, it is necessary to measure the exact amount of material he eliminates in the form of carbonic acid and other excretions.  Such experiments present many difficulties which have not yet been thoroughly overcome, but they have been attempted by several investigators.  For the purpose of such an experiment scientists have allowed themselves to be shut up in a small chamber six or eight feet in length, in which their only communication with the outer world is by telephone and through a small opening in the side of the chamber, occasionally opened for a second or two to supply the prisoner with food.  In such a chamber they have remained as long as twelve days.  In these experiments it is necessary to take account not only of the food eaten, but of the actual amount of this food which is used by the body.  If the person gains in weight, this must mean that he is storing up in his body material for future use; while if he loses in weight, this means that he is consuming his own tissues for fuel.  Careful daily records of his weight must therefore be taken.  Estimates of the solids, liquids, and gases given off from his body must be obtained, for to carry out the experiment an exact balance must be made between the income and the outgo.  The apparatus devised for such experiments has been made very delicate; so delicate, indeed, that the rising of the individual in the box from his chair is immediately seen in a rise in temperature of the apparatus.  But even with this delicacy the apparatus is comparatively coarse, and can measure only the most apparent forms of energy.  The more subtle types of energy, such as nervous force, if this is to be regarded as energy, do not make any impression on the apparatus.