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and nitrogen, in the proportion, by volume, of one-fifth of the former to four-fifths of the latter, and, besides these, carbonic acid, or fixed air, which exists in the free atmosphere in the proportion of about four parts to ten thousand.

In the small proportion in which carbonic acid exists in the free atmosphere it produces no evil effects; but in larger quantities it is not only dangerous, but frequently fatal. Being heavier than the other gases of the atmosphere, it is usually found in excess in low or confined places, such as mines, grottoes, and wells, and in the holds and steerages of ships, and in unventilated apartments generally. Under all such circumstances it is more or less dangerous to life. The bad air at the surface of close rooms is carbonic oxid, the product, usually, of burning gas and bad arrangements for warming. This, being the lightest of the deleterious gases, in close rooms rises to the surface.*

Pure oxygen will sustain life but a short time, owing to its stimulating qualities; it requires dilution, which seems to be the purpose of nitrogen, which cannot sustain life at all, and alone is deadly from its negative qualities. Carbonic acid pure is not respirable. If an attempt be made to inhale it, the glottis closes and prevents it from entering the lungs. When diluted with twice as much or more of air, it ceases to produce that effect upon the glottis, and is permitted to enter the lungs and the blood, and acts as a narcotic poison directly upon the brain. It is not possible to state how large a proportion of this gas may be present in the air without danger; it doubtless differs with different individuals. By experiments on animals it has been shown that an atmosphere containing 5 per cent. of carbonic acid is fatal in about thirty minutes.

Facts abundantly prove that respired air, or the air of occupied apartments containing of carbonic acid more than one volume per 1,000, is dangerous to health. Such air contains, besides the excess of carbonic acid, not infrequently the more deadly carbonic oxid, dead and decomposing animal matter, and other mephitic gases and exhalations arising from defective sewerage or vaults, but it is deficient in its very first life-sustaining property-oxygen-conditions predisposing to and frequently the cause of many fatal diseases.

The average amount of oxygen consumed by a healthy individual is half a cubic inch to every respiration, which in a day amounts to upwards of 25 cubic feet; and, as oxygen constitutes but one-fifth of the volume of the atmosphere, a single individual renders 125 cubic feet of air unfit for respiration every twenty-four hours by the abstraction of oxygen alone. Meanwhile there is exhaled by the lungs about 15 cubic feet of carbonic acid, 30 ounces of watery vapor, and an indefinite amount of organic matter, variously estimated at from 10 to 240 grains.

The whole quantity of air actually respired in twenty-four hours by a healthy person is about 400 cubic feet. This contains, when once passed through the lungs, 5 per cent. of carbonic acid, or more than one hundred times as much as it did when it entered them. It is plain, therefore, that in order to reduce respired air to the same standard of purity it had before it was respired, and to keep it so, the supply of fresh air must be at the least equal to one hundred times the volume of that which is thrown out, and upon this condition rests the importance of air-space, the space required depending upon circumstances. For various practical purposes the limits of space may vary from 300 to 4,000 cubic feet, the smallest proportion being the exaction for lodging-houses and the largest for hospitals, making due allowance in all cases for space occupied by furniture. And no deviation whatever should be made on account of children, whether in regard to the different members of a family or a school

room.

The smaller the space, the greater the necessity of, and the larger the opening required for, the admission of fresh air. If two or three hundred cubic feet only be allowed to the individual, the air must be changed every fifteen or twenty minutes, provision for which necessitates a draught and in cold weather great waste of heat. Specific gravity: Oxygen, (unit,) 1,000; atmospheric air, in the aggregate, 1105.63; nitrogen, 971.37; carbonic acid, 1524.5; carbonic oxid, 971.2.-Graham.

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Hence it is evident that the danger of "taking cold" in a small room, if it is kept ventilated, is much greater than it is in a large one. To reduce the gaseous components of respired air to their natural proportions and to neutralize its deleterious qualities, every person requires from 2,000 to 2,500 cubic feet of fresh air every hour.

To admit this amount of fresh air into a room is not as difficult as persons generally suppose. It has been calculated that with ordinary exposure an open space equal to five inches in the square will admit the passage of 2,000 cubic feet of air hourly; this, of course, implies that there should be an equal amount of open space for the escape of the air displaced. If, therefore, an ordinary window of three feet wide be open about an inch and a half at the top, and there be a chimney-flue in the room, the purpose is accomplished. Or the same by two windows on opposite sides of the room; or, it may be by crevices equal to this space about a door, in co-operation with one window. The multiplication of persons, it is plain, requires a corresponding multiplication of means.

In the aeration of the blood the organs of circulation and respiration are both no less essential to the maintenance of life than they are to each other. Their combined functions constitute the only means of admitting air into the body. And these functions must co-operate and be maintained, without intermission for one single minute, from birth until death. And yet, they have rest; the heart reposes about one-fourth of its time, and the lungs about one-third, but the periods of repose are too short to allow of any escape from a dangerous atmosphere.

The amount of blood in the human body constitutes about one-eighth of its entire weight, but it is variable within certain limits, depending upon the time and amount of food taken. Air is drawn into the lungs through the windpipe or trachea, which divides and subdivides into numerous smaller tubes leading to the air-cells, which, in the aggregate, constitute the lungs, situated one on each side of the chest and the heart between. The number of the air-cells has been estimated at seventeen millions, presenting a surface, if spread out, equal to about 22,000 square inches, or thirty times the surface of the whole body. The lining membrane of the air-cells, attenuated to the thinness of a cobweb, is the medium by which the air communicates with the blood. But the air in the lungs is not wholly changed with every breath. It cannot suddenly penetrate the membrane which separates it from actual contact with the blood and effect the required change in a moment. On the contrary, the air-cells are constantly full, the quantity contained being from 20 to 30 cubic inches, and of this the amount changed with each breath is only about one-tenth. Each fresh supply mixes with that which remains, and the change goes on incessautly, while that which is breathed out, although about the same in quantity, is, as already shown, very different in its properties. If the wall of an air-cell be examined with the microscope, it will be found to be covered with a net-work of exceedingly small blood-vessels, called capillaries, but much finer than hairs and so closely packed together that the interspaces are smaller than the vessels. These little vessels are the communicating extremities of larger ones, beginning and ending in the heart. At every beat of the heart, blood is sent into the pulmonary artery, and through it into the capillaries, where it is brought into contact with the lining membrane of the air-cells and through it exposed to the air; thence it returns again to the heart by the continuation of the capillaries into the pulmonary veins.

It is calculated that at each pulsation of the heart not less than one-twenty-seventh of all the blood in the body passes into the lungs; three times every minute the whole mass of blood is passed through the lungs and exposed to the air. Measured at each circuit, the whole quantity of blood so exposed in a day amounts to fifty-seven hogsheads, and, by weight, five hundred and forty pounds every hour, or twelve thousand nine hundred and sixty pounds in a day.

The quantity of fresh air imbibed by this exposure of the blood amounts to 616 cubic izches, or about two and a quarter gallons every minute, or upwards of two hogsheads pe: hour.

Life has often been compared to a burning flame, a sort of combustion, which, like fire, can never be sustained without the consumption of fuel, and, failing this, it flickers out, never again to be rekindled unless new life be given. The simile is in some respects marvelously perfect. Both flame and life depend upon air. Most persons have witnessed the experiment of placing a lighted candle or a taper under a bellglass, and know the result; that at first it burns brightly, gradually becomes feeble, and finally goes ont altogether. If instead of flame a bird or a mouse be placed under the glass, the effect on its life is precisely the same. In both cases the air is devitalized; it is not all used up, but that which is left will neither support a flame nor sustain life. A large proportion of the oxygen has been consumed and the proportion of carbonic acid and moisture increased. In the one case oxygen has been used to support combustion and in the other to sustain life; and air which has been respired, or in which anything has been burned, is always deficient in oxygen and contains an excess of carbonic acid and moisture. So far, then, as these conditions apply, every living animal represents combustion. In the free atmosphere, no creature ever suffered for the want of oxygen or from an excess of carbonic acid; but in crowded and unventilated rooms great harm often results from both.

Brain-culture is environed by the school-room. Upon the condition and management of the school-room depends the quality of the brain, and the brain is the soil of subsequent endowments. Education is the fruit; it contemplates a continuance of mental discipline and exertion far beyond the limits of the school-room or college-life. By education is acquired the mental and moral power to restrain the feelings, affections, propensities, and passions, so that none of these may ever gain the mastery over the intellect, a power which can never be acquired without proper brain-culture. A fruitful harvest can never come of an impoverished soil. Most of the anxieties and miseries of life result from the want of a sound and strong brain; and, as we trace back these to their source, they all seem to depend on the want of power to regulate impulse and feeling. A well-cultivated brain is unquestionably the true road to exalted virtues, and the union of a sound intellect and moral power the only stable foundation of true wisdom, by which health becomes, next to eternal salvation, the most important object of life.

A pure atmosphere is the first need of the school-room. Without it none of the vital functions can be sustained in health. We have seen the wonderful activity with which the functions of life are performed; that within twenty seconds a poisonous gas drawn in with the breath permeates every tissue of the body; that every single respiratory act multiplies the carbonic acid a hundredfold. No teacher, surely, will fail to appreciate the importance of these phenomena; nor should he fail to teach them to his pupils. A new series of questions in arithmetic should be devised for their inculcation, such as: If half a cubic inch of oxygen be consumed every respiration, how many respirations will it take to consume 25 cubic feet? If air that has been once passed through the lungs contains 5 per cent. of carbonic acid, how many volumes of atmosphere will it require to reduce it to four parts per ten thousand? If a single pupil breathes 70 cubic feet of air in four hours, how many cubic feet will be required for 600 pupils seven hours? If a closet of 300 cubic feet capacity requires 2,000 cubic feet of fresh air every hour to purify the air sufficiently for one individual, how many cubic feet of air will be required every hour to purify the atmosphere of a school-room 40 by 35 by 12 containing 75 pupils? Many other questions of similar practical utility will readily suggest themselves to the thoughtful teacher.

I cannot better close these remarks than by calling your attention to the recent action of the Rhode Island State Medical Society, as being eminently worthy of your serious consideration. This action may not meet with your approval in all its particulars, but it is commendable as being a practical and definite application of general principles and a suggestion to all thoughtful persons who are in any way responsible for the modes and methods of education:

"Whereas, although the present school-system has been brought to a high degree of

completeness in intellectual culture and to an exalted position of which its friends and the community may well be proud, yet, entertaining for its welfare a profound interest and viewing it as we do from a physical stand-point and believing that in the haste for intellectual culture the physical is too much neglected, the nervous system is developed to the omission of other portions of the body, thus giving rise to a long train of ills and producing an unsymmetrical and distorted organization in the young, entirely unfitted for the stern duties of life: Therefore,

"Resolved, First, that physical culture is of primary importance in our public schools and that gymnastic exercise should be made a part of our school-system.

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'Secondly, that the Kindergarten-system' should be ingrafted upon our publicschool-system.

"Thirdly, that the school-buildings should not exceed two stories in height.

"Fourthly, that 300 cubic feet of space and 25 square feet of floor-space should be the minimum for each child in a school-room in connection with good ventilation.

"Fifthly, that proper warmth and pure air are of the first importance, and should always be considered before ornamentation.

"Sixthly, that scholars should not maintain the same position more than half an hour at a time.

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Seventhly, that two short sessions, daily, are better than one long one.

"Eighthly, that no child should be admitted into our public schools, as now conducted, under 7 years of age.

"Ninthly, that under 12 years of age, three hours a day, and for 12 years and over, four hours a day, is sufficiently long confinement to mental culture.

"Tenthly, that study out of school should not usually be permitted.

"Eleventhly, that all incentives to emulation should be used cautiously, especially with girls.

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Twelfthly, that the half-time system' should be introduced into our public schools." The PRESIDENT. The subject is now before the department for discussion, and I would especially invite gentlemen of the medical profession who have favored us with their presence this evening to participate.

Dr. C. C. Cox, of the board of health of Washington, said:

I had hoped, Mr. President, that some other member of the profession better qualified than myself would have availed himself of the opportunity thus presented to respond. I appreciate, however, the privilege that is extended to me of expressing my personal gratification with the proceedings on this occasion.

I have been attracted to this room, sir, not so much by the importance of the subject announced for discussion, nor yet by the wide-spread and well-known reputation of the distinguished gentleman who has treated this subject so ably and exhaustively this evening, as by the evidence, the pregnant evidence, accorded, that this body of intelligent educators has been penetrated by a large share of that wide-spread and growing interest, which is felt at this day as it has never been felt before, in the practical relation of public teaching to the most important development of our race in every regard, and for the dearest interests which lie at the foundation and constitute the basis of our prosperity as individuals, as communities, and as nations.

I say, sir, that the interest of this subject and the reputation of the lecturer would, under ordinary circumstances, be sufficient inducements for me to be present here or anywhere; but I am more impressed with the fact that these intelligent gentlemen present, representing one of the great interests in this country and forming but a part of the wide-spread feeling which exists everywhere, are, as I have said, penetrated by a deep interest in what they know to be one of the most essential elements in the successful prosecution of public education and instruction of youth.

We know that a healthy mind cannot exist in an unhealthy body, and the history of literature and the science of the whole world demonstrate it. Where do you find

thoughts so fresh and glowing and philosophic as come to us from the clime of Scotland, where every man is endowed with strength and where exercise is regarded as one of the necessary adjuncts, as essential as eating and sleeping or any other operation of life.

I was very forcibly impressed, sir, by the resolutions with which the distinguished lecturer closed his remarks. Those resolutions are in accord with the views which I have always entertained. I think no more disagreeable precedent exists in connection with the history of education in this country than the so-called infant-schools which existed some years ago. The intelligence of the age has arrived at the importance of cultivating at that period the physical foundation or basis upon which all mental enlargement and all mental advancement exist. We all know, as physicians and medical men, that a child is born into the world with a large preponderance of the nervous element. He has a large head, a big brain, while the other parts of the system, the muscular and other portions of the constitution, are not developed in a corresponding ratio; and hence the extreme sensitiveness that attaches to the young child in connection with the peculiar nervous development. The object of that period is not to stimulate the nervous system by too much culture other than that which nature shall suggest in the simple operation of play and exercise, which the child most wants. The effect of such a course of stimulation is still further to oppress the powers and the peculiar condition of the system upon which mental success depends. And just as certainly as the child is forced into that culture, at that age, just as certainly as that system is adopted, just so certainly do you find the child the subject of premature mental decay. The vital powers are taken away, and he drops: a monument to the folly that has forced his mind into exercise before his body is prepared for development.

Now, sir, to the consideration of the principle inculcated by those resolutions as to the time at which the child should be introduced into the school. The number of hours required for the first few years I consider of great importance, and this cannot but be indorsed by this body, every letter and every word of it. Then, sir, the practical relations hinge upon the school-house itself; the architectural construction of it, the amount of space, of cubic feet of atmosphere required for the respiration of each individual, the heating of the house, the time of exercise, the peculiar arrangement of stndy-these are all practical subjects, which cannot be too fully and too strongly enforced in this day of ours.

These subjects have been elaborately discussed, particularly that in regard to the importance of pure air and plenty of it.

It is not my purpose to take up the time of this body by adding one word to what has been so ably and properly said. I merely arose to make my acknowledgment for the courtesy extended by the president to gentlemen not members of the convention to join in the purposes for which this meeting is assembled on this occasion, and as a member of the board of health of this city, and as one of its humblest representatives.

General EATON. It is my purpose to offer a few observations upon this subject, but not to discuss it.

Few careful observers in this country have failed to note the difference between a country school-house and a city school-house. Those who have attended schools in both have felt the difference and those who have passed beyond this personal experience into a study of the relations of health and education have been startled at every step by the results of the comparison. No one can enumerate the times that Mr. Mann and Dr. Barnard were compelled to call attention to lack of air and defects in furniture and construction. They and their coadjutors smote down certain evils within their reach, but beyond these evils. still exist. In our cities, while we have erected many fine school-houses,

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