formation of chemical compounds in both animate and inanimate nature, and the chemist only asked for a knowledge of the constitution of any definite chemical compounds found in the organic world in order to be able to promise to prepare it artificially. Seventeen years elapsed between Wohler's discovery of the artificial production of urea and the next real synthesis, which was accomplished by Kolbe, when in 1845 he prepared acetic acid from its elements. Since then a splendid harvest of results had been gathered in by chemists of all nations. In 1834 Dumas made known the law of substitution, and showed that an exchange could take place between the constituent atoms in a molecule, and upon this law depended in great measure the astounding progress made in the wide field of organic synthesis.

Perhaps the most remarkable result had been the production of an artificial sweetening agent, termed saccharin, 250 times sweeter than sugar, prepared by a complicated series of reactions from coal tar. These discoveries were not only of scientific interest, for they had given rise to the industry of coal tar colors, founded by our countryman Perkin, the value of which was measured by millions sterling annually. Another interesting application of synthetic chemistry to the needs of everyday life was the discovery of a series of valuable febrifuges, of which antipyrin might be named as the most useful.

An important aspect in connection with the study of these bodies was the physiological value which had been found to attach to the introduction of certain organic radicals, so that an indication was given of the possibility of preparing a compound which will possess certain desired physiological properties, or even to foretell the kind of action which such bodies may exert on the animal economy. But now the question might well be put, Was any limit set to this synthetic power of the chemist? Although the danger of dogmatizing as to the progress of science had already been shown in too many instances, yet one could not help feeling that the barrier between the organized and unorganized worlds was one which the chemist at present saw no chance of breaking down. True, there were those who professed to foresee that the day would arrive when the chemist, by a succession of constructive efforts, might pass beyond albumen, and gather the elements of lifeless matter into a living structure. Whatever might be said regarding this from other standpoints, the chemist could only say that at present no such problem lay within his province.

Protoplasm, with which the simplest manifestations of life are associated, was not a compound, but a structure built up of compounds. The chemist might successfully synthesize any of its component molecules, but he had no more reason to look forward to the synthetic production of the structure than to imagine that the synthesis of gallic acid led to the artificial production of gall nuts. Although there was thus no prospect of effecting a synthesis of organized material, yet the progress made in our knowledge of the chemistry of life during the last fifty years had been very great, so much so indeed that the sciences of physiological and of pathological chemistry might be said to have entirely arisen within that period.

CHEMISTRY OF VITAL FUNCTIONS.

He would now briefly trace a few of the more important steps which had marked the recent study of the relations between the vital phenomena and those of the inorganic world. No portion of the science of chemistry was of greater interest or greater complexity than that which, bearing on the vital functions both of plants and of animals, endeavored to unravel the tangled skein of the chemistry of life, and to explain the principles according to which our bodies live, and move, and have their being. If, therefore, in the less complicated problems with which other portions of our science have to deal, we found ourselves often far from possessing satisfactory solutions, we could not be surprised to learn that with regard to the chemistry of the living body—whether vegetable or animal—in health or disease, we were still farther from a complete knowledge of phenomena, even those of fundamental importance.

Liebig asked if we could distinguish, on the one hand, between the kind of food which goes to create warmth and, on the other, that by the oxidation of which the motions and mechanical energy of the body are kept up. He thought he was able to do this, and he divided food into two categories. The starchy or carbo-hydrate food was that, said he, which by its combustion provided the warmth necessary for the existence and life of the body. The albuminous or nitrogenous constituents of our food, the flesh meat, the gluten, the casein out of which our muscles are built up, were not available for the purpose of creating warmth, but it was by the waste of those muscles that the mechanical energy, the activity, the motions of the animal are supplied.

Soon after the promulgation of these views, J.R. Mayer warmly attacked them, throwing out the hypothesis that all muscular action is due to the combustion of food, and not to the destruction of muscle.

What did modern research say to this question? Could it be brought to the crucial test of experiment? It could; but how? In the first place, we could ascertain the work done by a man or any other animal; we could measure this work in terms of our mechanical standard, in kilogramme-meters or foot-pounds. We could next determine what was the destruction of nitrogenous tissue at rest and under exercise by the amount of nitrogenous material thrown off by the body. And here we must remember that these tissues were never completely burned, so that free nitrogen was never eliminated. If now we knew the heat value of the burned muscle, it was easy to convert this into its mechanical equivalent and thus measure the energy generated. What was the result?

Was the weight of muscle destroyed by ascending the Faulhorn or by working on the treadmill sufficient to produce on combustion heat enough when transformed into mechanical exercise to lift the body up to the summit of the Faulhorn or to do the work on the treadmill?

Careful experiment had shown that this was so far from being the case that the actual energy developed was twice as great as that which could possibly be produced by the oxidation of the nitrogenous constituents eliminated from the body during twenty-four hours. That was to say, taking the amount of nitrogenous substance cast off from the body, not only while the work was being done, but during twenty-four hours, the mechanical effect capable of being produced by the muscular tissue from which this cast-off material was derived would only raise the body half way up the Faulhorn, or enable the prisoner to work half his time on the treadmill. Hence it was clear that Liebig's proposition was not true.

The nitrogenous constituents of the food did doubtless go to repair the waste of muscle, which, like every other portion of the body, needed renewal, while the function of the non-nitrogenous food was not only to supply the animal heat, but also to furnish, by its oxidation, the muscular energy of the body. We thus came to the conclusion that it was the potential energy of the food which furnished the actual energy of the body, expressed in terms either of heat or of mechanical work.

But there was one other factor which came into play in this question of mechanical energy, and must be taken into account; and this factor we were as yet unable to estimate in our usual terms. It concerned the action of the mind on the body, and although incapable of exact expression, exerted none the less an important influence on the physics and chemistry of the body, so that a connection undoubtedly existed between intellectual activity or mental work and bodily nutrition. What was the expenditure of mechanical energy which accompanied mental effort was a question which science was probably far from answering; but that the body experienced exhaustion as the result of