tions. But the functions of a vital organism are themselves vital. What, then, is the meaning of "vital" as applied to a function? Fortunately, the answer is not difficult. "Life," says Küss, the distinguished Strasburg physiologist, "is all that can not be explained by chemistry or physics." Guided by such a definition the work of the physiological investigator is simple. He has only to test each separate operation which he finds going on in the organism, and to declare whether it be chemical or physical, If it be either, then, since each function is non-vital, the entire organism must be non-vital also. Hundreds of able investigators, provided with the most effective appliances of research, are now in full cry after the life-principle. Naturally, a vast amount of collateral knowledge is accumulated in the process. The quantitative as well as the qualitative relations of things are fixed and many important facts are collected.
With the object in view thus clearly defined, we are not surprised that great progress has been made. A vital process, like the catalytic ones of the older chemistry, was found by such research to be simply a process which, for want of sufficient investigation, is not yet understood. While therefore, undoubtedly, much work yet remains to be done in the realm still called vital, the prophetic vision is already bright which will witness the last traces of inexplicable phenomena vanish and the words expressing them relegated to the limbo of the obsolete.
As a first result of recent work, the living organism has been brought absolutely within the action of the law of the Conservation of Energy. Whether it be plant or animal, the whole of its energy must come from without itself, being either absorbed directly or stored up in the food. An animal, like a machine, only transforms its energy. Lavoisier's Guinea-pig placed in the calorimeter gave as accurate a heat-return for the energy it had absorbed in its food as any thermic engine would have done. But the parallel goes further. The mechanical work of an engine is measured by the loss of its heat and not of its substance. So the mechanical or intellectual work of a living being is measured by the amount of food rather than the amount of tissue which is burned. The energy evolved daily by the human body would raise it to a height of about six miles.
But, besides heat, work may be the outcome of the organism; and this through the agency of the muscles. Their absolute obedience to mechanical law in their mode of action has been admirably established by Haughton. The work a muscle does, it does in contracting. It is to the mechanism of muscle-contraction that we are indebted for another illustration of our subject.
When work is done by a muscle in contracting, three changes are observed to take place in its tissue: First, there is a loss of its electric tension; second, there is an evolution of heat in it; and, third, carbon dioxide appears there, and its reaction, before neutral, becomes acid.
