Poisonous emanations. General view of the causes of disease.

the human system is often subjected, that are largely destructive of health and life. They arise from decomposing filth of various kinds. Besides predisposing the system to the action of contagious and epidemic causes of disease, they also of themselves create disease. It is these emanations that render the close air of a crowded city, especially in its narrow lanes, so impure and fairly poisonous. And this impurity of the air is one of the chief causes of the difference in disease and mortality between the city and the country. The difference is greater than is generally supposed. It has been found by statistics in England, that there are 24 per cent. more deaths from consumption, and 55 per cent. more deaths from typhus, in cities than in the rural districts, and the mortality from the diseases of childhood is twice as great in the city as in the country. In what way these emanations act we know not. But, although much is to be attributed to a mere want of ventilation, that is, to a lack of oxygen, there is no question that these emanations often act as positive poisons to the system.

674. In developing the principles of hygiene, I have noticed many of the prominent causes of ill health and disease. They are chiefly these: 1. A disregard in various ways of the rules relating to the digestive process. 2. Compression of the chest, especially during the period of growth. 3. Deficiency in the supply of pure air to the lungs. 4. Failure to guard properly against the influence of cold and heat, chiefly the former. 5. A lack of active exercise in the open air. 6. Overworking the muscles. 7. Errors in the management of the moral and intellectual powers. 8. The influence of such articles as alcohol and tobacco. 9. Emanations from decomposing filth. It is well thus to look at these causes grouped together, endeavoring to give to each its due prominence. For various and exclusive views are often taken of this subject. Quite commonly some of these causes are kept entirely out of view, while others are strongly pressed upon our attention. Disease is generally a very compound result, produced by a concurrence of several of these causes, and sometimes even of all of them.

675. These causes of disease, it will be observed, are more or less under our control. Some of them are entirely so. A knowledge of their operation, and an earnest endeavor to remove them, would, therefore, vastly diminish the amount of ill health and disease.

Our control over the causes of disease. Preventive and curative measures.

676. It is true that there are some other causes of disease, of which we know but little, and over which we have little or no control. Such are the causes of various contagious and epidemic diseases. But these really produce a much less amount of disease than the causes which I have mentioned. Their action is occasional, and confined to localities; not continual, and in all places. And besides, they may to a great extent be shorn of their power, by guarding against those causes of disease which are more or less under our control. It is those who neglect to do this that commonly become most readily the victims of contagions and epide

mics.

The

677. There is much interest in the community in regard to the cure of disease, but there is a blind indifference to its prevention. And yet vastly more can be done in the diminution of disease by preventive than by curative measures. ravages of consumption, for example, can undoubtedly be greatly lessened by preventing the operation of its principal causes; and yet what is said about these causes is little heeded, and the public attention is engrossed with the delusions of consumption-curers. It is emphatically true of this malady, that multitudes more can be saved by preventive measures than by curative ones. Against no disease can hygiene achieve greater victories than this. The neglect to use preventive measures against this and other diseases arises chiefly from an ignorance of the principles on which these measures are based. The prevalent indifference, therefore, on this subject can never be fully removed, till the general introduction of Physiology as a study into our schools shall make these principles familiar to the mass of the community.

APPENDIX:

CONTAINING

DIRECTIONS TO TEACHERS FOR THE USE OF THE BOOK, AND QUESTIONS.

In order to be able to teach from this book properly, the teacher should himself study all of it thoroughly before he begins his instruction. If he merely keep a little in advance of his class, he will fail in his conceptions of the general scope and plan of the book. If the interest of the subject awaken in him and in his pupils a spirit of inquiry, there will be a continual looking forward to points which are explained and illustrated further on in the book. Now if the teacher has made himself master of all the subjects treated of, instead of turning off the inquiry of a scholar without an answer, or even the promise of an answer in the future, or endeavoring to clear up the points about which inquiry is made, which of course he can do, under the circumstances, in an imperfect manner at the best, he can satisfy the scholar by informing him that these points will be found explained in their proper place at a future stage of the investigation. I have aimed to have every topic treated of in its right place in the development of the general subject, and the teacher should be thoroughly master of the whole book at the outset, in order that he may fully carry out my plan in the mode of developing the topics to the minds of his pupils.

It must be obvious to any teacher that he can teach the minutia of the subject with more of interest, to say nothing of thoroughness, if, while doing it, he takes in the general views presented, and has in mind the relations of the particular topics in hand to other branches of the subject. Indeed it will be profitable occasionally for the teacher to afford the scholar some glimpses of the interesting fields to be explored further on, taking care, however, not to anticipate so much, as to mar the natural method and order of developing the whole subject, which I have taken such especial care to observe in the preparation of the work.

The teacher should read the book through in course. If, instead of doing this, he opens to some chapter in the middle or latter part of the book, he may get the impression that too high matters are treated of, and that the minds of his pupils are not competent to understand them. They cannot be understood unless there be a preparation of mind for them; and just this preparation is aimed at in the first part of the book. And besides, it is quite important that the subjects treated of

should be developed to the mind of the teacher in the same order ir which they are to be developed to the minds of his pupils.

In the engravings clearness has been aimed at rather than beauty. Yet I should not do the engraver justice if I did not say, that in beauty they are generally quite equal to those which we find in our standard professional works on physiology. It is to be borne in mind that woodcuts cannot represent correctly the beauty and delicacy of living structures. These can be realized only by seeing the structures themselves. Another thing to be kept in mind is, that parts which are represented in engravings with definite lines for the sake of distinctness, are ordinarily not thus distinct in the structures. To make them so, the dissectingknife must separate them, and take off the cellular substance, which, as the general packing material of the body, everywhere connects adjacent parts together.

The teacher can be aided very much in giving his scholars a correct idea of different organs, by presenting to them organs taken from the bodies of animals. Thus, in giving them an idea of the lungs, the lungs of a calf or a sheep can be used. A pipe may be fastened into the windpipe; and by blowing into this, you can show how the lungs are inflated. An idea of the appearance of the human brain can be given by means of the brain of a calf, or any other animal of sufficient size. An ox's heart may be used in showing the structure and arrangement of the valves and other parts of that organ, for they are essentially the same as in man. A very good idea of the arrangement of the cartilages that make up the larynx, can be obtained from the larynx of an ox or COW. The general shape and arrangement are the same as in man. It is some trouble to clear the parts of muscular substance, but the teacher can get some physician or medical student to do it for him. When the preparation is once made, it can be dried for permanent use. I have one which I made twenty-five years ago. In drying, it will be necessary to keep the wings of the thyroid cartilage apart by a wedge, and the supple epiglottis must be placed in such a position as not to interfere with a view of the interior of the larynx. The large eye of the ox can be made use of to show the various parts of that organ, and also to show the formation of the images of objects on the retina.

One great advantage of thus using parts from different animals is, that a taste is given for the examination of the phenomena of life, with its wonderful mechanisms, wherever they may be seen. All living nature thus becomes full of suggestive interest to the young student.

There are some things of which plates can give no correct idea. Such, for example, is the cellular membrane. The attempt to represent it is made in most books on physiology, but it is an entire failure. I have a plate representing its cells as seen in a dried preparation under the microscope; but to give the scholar an idea of it as it appears to the naked eye in its natural condition, I refer him to it as seen in any common piece of meat between the muscles and between the fibres of each muscle. The teacher can use a piece of meat for this purpose. The difference between muscles, tendons, and ligaments can be shown in the

same way.

Those figures which are mere diagrams it will be well for the scholar to draw on the blackboard, and his skill in description and remark may be exercised for his own benefit and for that of the class. He should

be trained in this exercise in such a way, that he will acquire the power of giving well-proportioned and well-arranged descriptions, without the aid of prompting by minute questions from the teacher.

It will be proper to say something of the use which should be made of the questions that I have prepared. I have two reasons for not placing them at the foot of the page. One reason is, that the book is designed for general reading as well as for instruction. But the chief reason is, that I wish to prevent a too free use of questions on the part both of teacher and scholar. The marking with the pencil of parts which contain the answers to the questions, so often done in our schools, should never be permitted by the teacher, for reasons that I need not stop to notice.

The scholar should read the text at first without reference to the questions; and then the questions can be made use of, perhaps with profit, to fix definitely in the mind the principal points that are brought out. It will be a useful exercise for the scholar, after reading a page or two, to think over the main points, and then see by the aid of the questions whether any important point has escaped his recollection, or failed to make the proper impression on his mind.

The questions that I have constructed will, I think, be found to be fitted to the great majority of scholars. But of course the teacher will vary them to suit the different capacities and mental attitudes which he finds in his class.

It is best not to have an uniform mode of asking questions, even with the same scholar. Variety should be given to the mode of hearing the recitation. Sometimes the questions should be minute, and at other times the mind of the scholar should be left to go on with as little leading as possible.

The scholar should be encouraged occasionally to give the substance of a whole paragraph, or even of more than this. In doing so, any failure in arrangement or proportion can be noticed by the teacher, for the benefit not only of the scholar that is reciting, but also of the whole class. The general scope of an argument may also be given in the same way, and the manner of doing it be made the subject of criticism.

The numbers attached to the questions refer to the pages, this being more convenient to the scholar than a numbering by paragraphs would be, though of course it cannot be quite as definite in all cases.

35*