plan the sequence that best fits the season. In fact, the last use that a good teacher will make of any laboratory manual or text-book is that of following it slavishly. It is the hope of the authors, however, that the laboratory guides and the text descriptions which follow may be sufficiently suggestive to help some teachers to work out improved methods in biological instruction. In Appendix II will be found a suggested order of topics which the authors have found satisfactory.

Living organisms are to a large extent to be regarded as chemical engines so constructed as to liberate different kinds of energy. No one, of course, knows in any ultimate sense how even the simplest functions are performed by the simplest animals or plants. But it is utterly useless to attempt to teach biological functions without first presenting some of the elementary principles involved in physical and chemical phenomena. For this reason the first chapter in Plant Biology is devoted to the study of the Composition of Lifeless and Living Things. in Chapter III is a brief discussion of the structure of a common plant, and since cells are fundamentally alike in structure and functions in all living organisms, emphasis is laid early in the course on the essential characteristics of these cellular elements in plants. Another topic which necessarily recurs throughout plant, animal, and human biology is the principle of osmosis and its applications. The authors have inserted experiments which in their experience have helped to fix in mind this important principle and which demonstrate the necessity of digestion in plants and animals.

After this brief consideration of the fundamentals of plant composition, structure, and processes, Chapters V, VI, and VII are devoted to the study of the adaptations of plants for performing nutritive and reproductive functions. In

Chapter VIII are grouped experiments and descriptions the aim of which is to show various ways in which plants are propagated. This treatment presents only the briefest statement of underlying principles, since any extended discussion of this topic belongs to a course in agriculture.

In Chapters IX (Plants in their Relation to Human Welfare) and X (Plant Classification) the method of presentation is strikingly different from that adopted in the rest of the book, particularly so in the treatment of the spore-bearing plants. The authors believe that every pupil should be taught something of these simpler forms (especially bacteria), and that he should get as many of these facts as possible by observation. But to expect much laboratory work from young students on difficult microscopic forms like many of these cryptogams, is, we are confident, quite out of the question. We have, therefore, frankly abandoned the inductive method of study and have suggested that the laboratory work be largely in the nature of demonstrations. It is, of course, understood that if these forms are studied, the drawings and descriptions will be prepared from material in the hands of the student.

In our judgment there are few if any biological topics which are more important in their practical bearings than is that of bacteria. As commonly studied the disease-producing effects of these organisms are emphasized so much that boys and girls do not appreciate that all the work of the higher plants depends ultimately upon the activity of these low forms of fungi. In order to bring out this aspect of the work of bacteria and for other obvious reasons the structure, physiology, and economic benefit of these organisms are considered in the chapter on the relation of plants to human welfare, while their pathogenic effects are reserved for discussion in human biology.

The method of presentation in "Animal Biology" is somewhat different from that employed in "Plant Biology," for the reason that several widely different types of animals are studied. Limitations of time compel a rigid and somewhat narrow selection of groups for intensive study, and only those functions of each animal are considered which have some relation to human biology, or which have a broad, economic bearing. Thus insects are discussed largely because of their injurious or beneficial effects upon mankind; birds and fishes, because of their economic importance, and because of the great need for their conservation; and one-celled animals because of the light they throw on cellular processes. Certain other somewhat less important topics are considered incidentally; for example, protective resemblance and metamorphosis among insects, and the striking adaptations of structure to function in the bills, feet, and feathers of birds.

The animals suggested for additional study, if time permits, are representative mammals, reptiles, amphibia, arthropods, molluscs, worms, and cœlenterates. In many classes there are students who can work faster than the others, or who are interested in pursuing further their biological studies. Such students may be directed in carrying on some of these studies either in class or outside of school hours. In any case, students are likely to acquire considerable information by reading these textbook descriptions and studying the illustrations.

All the work of the year should lead up to and culminate in human biology. Here, too, however, many important topics must be treated only superficially, or altogether omitted, on account of lack of time. The authors believe that in this, the most important part of the course, practical hygiene should be taught as effectively as possible, and that the necessity for good food, pure air, varied exercise, and suffi

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cient sleep should be continually emphasized. If boys and girls can be led to conform their daily habits to the principles of healthy living, the course in biology will have its highest justification.

In the treatment of Stimulants and Narcotics, the authors have tried to state in simple language the conclusions of experts regarding the effect of tobacco and alcohol, and to present the strongest scientific arguments against the use of these substances which are so injurious to growing youths.

No study of human biology should be allowed to leave in the mind of the student the idea that he is merely a chemical engine adapted only for the generation of a certain amount of physical energy. The primary object of all secondary education should be the development of character and efficiency, and the true teacher ought to find opportunity again and again to touch the individual life of the young student. Especially should this be true in the study of biology. Growing boys and girls ought to come to feel, as they have never felt, that they have in their keeping a most complex and wonderful piece of living machinery which can be easily put out of order or even wrecked. But, on the other hand, they should see that if the bodily machine is well cared for, it is capable of splendid work which may help to increase the sum total of human efficiency and happiness.

In the preparation of this book the authors have received a great many suggestions from the teachers in their own departments and those of other schools. Our thanks are due to Miss M. Helen Smith of the Manual Training High School, Brooklyn, N.Y., for several laboratory outlines which formed the basis of corresponding studies in the following pages. The authors have been especially fortunate in securing the constructive criticism of Dr. C. Stuart Gager, Director of the Brooklyn Botanic Garden of the Brooklyn Institute of

Arts and Sciences. He has carefully read all of the manuscript and the page proofs of the "Plant Biology."

We are indebted to Dr. H. J. Webber, Professor E. O. Fippin, and others at Cornell University, for valuable material and illustrations for the chapter on Plant Propagation. We wish, also, to express our hearty appreciation of the generous permission of Henry Holt & Co. to use some of the material published in Peabody's "Laboratory Exercises in Anatomy and Physiology." We are fortunate, too, in securing from the New York Botanical Garden photographs for the frontispiece, and for several fine cuts in the text, and from Professor E. M. East of Harvard University the cut for Fig. 52, "Plant Biology. Miss Mabelle Baker, Miss Clara Lang, Miss Margaret Cutler, and Miss Grace Gamble, students in our first-year classes, have kindly prepared for us the figures on which their several names appear.

We have been especially fortunate also in securing the assistance of experts who have read much of the manuscript of the "Animal and Human Biology" and many of the proof sheets. Dr. E. P. Felt, New York State Entomologist, Mr. E. R. Root, author of "A. B. C. of Bee Culture," and Professor Glenn W. Herrick of Cornell University, have given us valuable criticism of the chapter on Insects. Dr. W. T. Hornaday, Director of the New York Zoological Park, has read the chapters on Birds and Fishes. To Mr. J. M. Johnson, Head of Department of Biology of the Bushwick High School, we are also indebted for suggestions relating to Birds.

Much of the manuscript of the chapter on Foods received the careful criticism of the late Professor W. O. Atwater. Dr. William H. Park, Director of the Laboratories of the New York City Board of Health, and Dr. Thomas Spees Carrington, Secretary of the National Association for the Study and Prevention of Tuberculosis, have given invaluable