teaches us that it rests on a properly intellectual labor, in which the understanding participates as a useful counsellor and assistant, but without guiding it and without its being dependent thereupon.

In science, as well as in common life, the operations of the mind are executed not according to the rules of logic, but the conception of a truth, the idea of a process or the cause of a phenomenon, generally precedes the demonstration; the conclusion is not reached through the premises, but the conclusion goes before, and the premises are then first sought out as proof. In a conversation with a celebrated French mathematician, on the part which the imaginative faculty bears in scientific labors, he expressed himself to the effect that by far the greater number of mathematical truths are obtained, not by deduction, but through the inventive or imaginative power, and in this he had a view even to the properties of the triangle, the ellipsis, &c., which is saying little else than that the mathematician, as well as the physicist, can do nothing for his science without artistic endowment.

It is scarcely necessary to say that for deductive as well as inductive research, if any results are to follow, a certain extent of information is prerequisite; for the deductive research, a well-grounded knowledge of laws already discovered, to which previous reading and books are contributary; for inductive, a comprehensive acquaintance with material phenomena which is to be acquired in chemical, physical, and physiological laboratories. As schools, these last are a modern creation, and their influence in the development of all departments of physical science is, to the reflecting observer, a thing not to be questioned.

To an acquaintance with sensible phenomena or the knowledge of the nature and action of things, must be united in the case of the inductive inquirer, if he would duly resolve the problems presented to him, a memory for sensible phenomena, a memory, it might be said, of sight, taste, and smell, together with a certain degree of artistic expertness and dexterity. The broader and more comprehensive his knowledge of facts and phenomena, or, as it is usual to say, the greater his experience, so much the more will his labor be lightened; an experienced man makes much fewer experiments than the inexperienced, who must make himself acquainted with many phenomena which to the other are already familiar; to the former, indeed, for the attainment of many ends, numerous experiments would be superfluous, since the combination of processes and facts already within his knowledge, abundantly suffices.

In the solution of their respective problems, the deductive and inductive inquirer begin in the same manner; the one, like the other, starts from a complex idea of the understanding or the imaginative power, of which in general only a part is true, while the other parts rest on erroneous inferences or combinations. The deductive inquirer tests and experiments with intellectual conceptions in order to find the truth, just as the inductive inquirer does with sensible ideas in order to find the thing sought for; both, in the prosecution of their inquiries, strip away,

by testing and improving, what is false, and detect the parts which are wanting to complete the idea submitted to examination. The idea from which they set out is not unfrequently wholly false, and the true is first sprung in the course of the investigation. Hence, the doctrine of many of the greatest inquirers that the labor is everything, and that any theory may lead to truth, provided it gives the impulse to toil.

In deductive inquiry, it is the conviction of the correctness of a concluding idea (schluss-idee) which stimulates the understanding of the inquirer to its appropriate activity; and so with the experimental artificer, the conviction of the existence of a thing is the first and most efficacious incitement to the movements of the imaginative power; the discovery of a new fact or reaction, to which the idea of something before unknown, something useful or important for industry or life, attaches, is sufficient to awaken the conviction of its existence in many individuals, and it not unfrequently happens that it is in reality simultaneously discovered by several.

Understanding and imagination are alike necessary to our knowledge, and in science are alike authorized; they both have an allotted part in all problems of physics and chemistry, of medicine, of public economy, history and philology, and comprise each a certain space in its appropriate province. The part in which the imaginative faculty bears sway is proportionately wider and more comprehensive, as the positive knowl edge with which the understanding circumscribes it is more indeterminate and indistinct. Progress consists in this, that with the increase of knowledge, the conceptions which have sprung from the imagination vanish, and while in the first periods of science this faculty had undisputed ascendancy, at a later stage it subordinates itself to the understanding and becomes to the latter a helpful and willing servant.

Induction under the guidance of the imagination is intuitive and creative, but vague and extravagant; deduction under the guidance of the understanding analyzes and limits, and is definite and measurable.

One of the most essential characters of deductive inquiry in science. is measure, and the ultimate aim of all its labors is directed to an unalterable numerical expression for the properties of things, for processes and phenomena. Imagination compares and discriminates, but measures not, for measurement implies a scale, and that is a product of the understanding.

By the introduction of science into an art accrues an advantage, scarcely enough appreciated; that science abolishes art as such, and what is individual in it, while resolving it into rules which may be taught and learned; through a knowledge of which rules even the unproficient in business, industry, husbandry, and technics, is invested with the power of the most proficient, most skillful, and most experienced practitioner, who attains his aims by the shortest, surest, and most economical means. What before was proper to the individual bebecomes thenceforth the joint property of all.

ADDRESS ON THE RELATION OF FOOD TO WORK, AND ITS BEARING ON MEDICAL PRACTICE.

BY REV. SAMUEL HAUGHTON, OF DUBLIN.

MR. PRESIDENT AND GENTLEMEN: Man, like other animals, is born, grows, comes to maturity, reproduces his like, and dies, passing in his lifetime through a cycle of changes that may be compared to a secular variation, by a metaphor borrowed from the science of astronomy; while in his daily life he passes through a smaller cycle of changes that may be called periodic.

From the time of the publication of Bichat's celebrated Essay on Life and Death, it has been admitted that man and other animals possess a double life, animal and organic, presided over, respectively, by two distinct though correlated centers of nervous force; of these, one thinks, moves, and feels; the other merely cooks, receiving the food supplied, changing and elaborating it into elements suitable for the use of the animal life. In the lower forms of animals the organic life becomes almost coextensive with the whole being of the creature, which simply digests, assimilates, and excretes, but barely feels or moves; in the higher forms of animals, and more especially in man, the animal life dominates over the organic life, which becomes its slave, and exhibits the remarkable phenomena of mechanical force, of geometrical instinct, of animal cunning, and, finally, in man himself, produces intellectual work, rising to its highest form in the religious feeling that recognizes its great Creator, and bows in humility before Him. It is a simple matter of fact, and of every-day observation, that all these forms of animal work are the result of the reception and assimilation of a few cubic feet of oxygen, a few ounces of water, of starch, of fat, and of flesh.

The general question of the relation of food to work would involve a consideration of the possibility of throwing a bridge across the gulf that separates the organic from the animal life, so as to connect the products of nutrition (taken in its widest sense) with the work of every kind accomplished by the animal life, whether mechanical or intellectual. We resemble the spiders of the heather on a summer morning, that float their gossamer threads into the air from the summit of a branch, in the hope that some stray breath of wind may fasten them to a neighboring tuft, and enable the hungry speculator to extend the range of his rambles and his chance of food. Already a few feeble threads connect the chemistry of our food with the mechanical work done by our muscles; when these shall have been securely fastened, from the higher vantage

ground thus acquired, our little bridge of knowledge may possibly be extended to embrace the phenomena of the geometrical instinct of the bee, or the cunning of the beaver, and our successors may even dare to speculate on the changes that converted a crust of, bread or a bottle of wine, in the brain of Swift, Molière, or Shakespeare, into the conception of the gentle Glumdalclitch, the rascally Sganarelle, or the immortal Falstaff. At present such thoughts would be justly regarded as the dreams of a lunatic, and I must crave your indulgence for having mentioned them. The history of science is, however, filled with such dreams-some never realized, others converted by time into realities so commonplace that the genius of their originators is habitually forgotten or underrated.

During childhood and youth the food that we eat is used for the double purpose of building up the tissues of the bones, muscles, brain, and other organs of the body, and of supplying the force necessary for work done, whether mechanical or intellectual. In adult life the first use of food almost disappears, for the bones, muscles, brain, and other organs have already reached their full development, and act simply as the media of communication between the food received and the work developed by it.

Let us take, as illustrations, the muscles and brain, regarded as the organs by means of which mechanical and intellectual work is done. These organs resemble the piston, beam, and fly-wheel of the steam. engine, and, like them, only transmit or store up the force communicated by the steam in one case, and by the products of the food conveyed by the blood in the other case. The mechanical work done by the steamengine must be measured by the loss of heat experienced by the steam in passing from the boiler, through the cylinder, to the condenser, and not by the loss of substance undergone by the several parts of the machinery on which it acts. In like manner, the mechanical or intellectual work done by the food we eat is to be measured, not by the change of substance of the muscles or brain employed as the agents of that work, but simply by the changes in the blood that supplies these organs, that is to say, undergone by the food used in its passage through the various tissues of the body, before it is finally discharged in the form of water, carbonic acid, or urea.

The Divine Architect has so framed the animal machine, that moves and thinks, that the same blood which, by its chemical changes, produces movement and thought, also repairs the necessary waste of the muscles and brain, by means of which movement and thought are possible; just as if the steam that works an engine were able, without the aid of the engineer, to repair the wear and tear of its friction and waste spontaneously; but no greater mistake is possible in physiology than to suppose that the products of the changes in the blood by which mechanical or intellectual work is done are themselves merely the

result of the waste of the organs, whether muscles or brain, on the exercise of which that work depends.*

The ancients, who derived all their knowledge from observation, and not from experiment, were well aware of the double duty imposed upon food in early life-of producing both the secular and the periodic variations of the body, or, in other words, of promoting growth, and of developing work. Their practical knowledge is summed up by Hippocrates in the aphorism, "Old men bear want of food best; next those that are adults. Youths bear it least, more especially children, and of these the most lively are the least capable of enduring it."

The food consumed in twenty-four hours, including air and water, undergoes a series of changes of a chemical character before leaving the body, in the form of one or other of its excretions. Some of these changes develop force, and others expend force, but the algebraic sum of all the gains and losses of force represents the quantity available for work. This work must be expended as follows:

1. The work of growth, (secular.)

2. The work of maintaining heat, (periodic.)

3. Mechanical work, (periodic.)

4. Vital work, (periodic.)

During childhood and youth the work of growth is positive, for a cer tain proportion of the food used is employed in building up the tissues of the body instead of being expended in actual work; it is, in fact, "stored up" in the body, as vis viva is stored up by the fly-wheel of machinery, and constitutes a reservoir of force that may be called upon at an emergency requiring sudden expenditure of force, as in case of illness, or to supply the gradual wasting of old age. In adult life and in old age, the work of growth ceases completely, except so far as is necessary to repair, from day to day, the small wastes of the organs employed in work; so that nearly the whole of the food employed is expended on the periodic work of the body. Hence we can readily see the reason for the aphorism which asserts that food is more necessary for the young than for the old, and more required by those of a lively disposition, either of mind or body, than by others.

*The very skill with which provision is made for the repair of the waste of the organ used as the instrument of work may mislead the observer into supposing that the work itself may be measured by the waste of its instrument. Thus, it has been shown by Mr. A. Macalister, of Dublin, that the heart, which has imposed upon it the necessity of working day and night without ceasing, during life, is furnished with double the usual supply of blood through the coronary arteries, which are injected twice for every single beat of the heart. If, indeed, it were possible to assume that all muscles wasted equally for equal quantities of work, and also to measure separately the products of that waste, we might then assume the waste of the organ as the measure of its work. Neither of these assumptions, however, can be admitted, for it can be shown that different muscles act under different conditions more or less advantageously, so that equal wastes would represent unequal works; and, also, it is impossible to separate in practice the products of waste of muscles from those of the general changes of the blood.