CHAPTER XII.

THE USE OF THE MICROSCOPE IN THE STUDY OF PHYSIOLOGY 236

_The Law of Tissues--Necessity of the Microscope--Different kinds of Microscopes--Additional Apparatus--Preliminary Studies--The Study of Human Tissues--Tissues of the Inferior Animals--Incentives to Study._

APPENDIX.

POISONS AND THEIR ANTIDOTES 247

GLOSSARY 252

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LIST OF ILLUSTRATIONS

FIG. PAGE FRONTISPIECE, } VISCERA IN POSITION,} 1. Section of bone, 17 2. Structure of bone, magnified, 17 3. The skeleton, 18 4. Cells of cartilage, 20 5. Elbow-joint, 21 6. Spinal column, 22 7. The muscles, 24 8. Muscular tissue, magnified, 25 9. Biceps muscle of the arm, 26 10. View of knee-joint, 27 11. Appliance for strengthening the muscles, 35 12. Appliance for strengthening the muscles, 35 13. Parlor gymnasium, 36 14. Root and transverse section of hair, magnified, 43 15. Granules of potato starch, 61 16. Section of the trunk, 81 17. Section of a tooth, 82 18. Section of the jaws, 82 19. Section of the jaws--right side, 84 20. Structure of a salivary gland, 87 21. Head of a horse, showing salivary gland, etc. 87 22. Section of chest and abdomen, 90 23. Organs of digestion, 91 24. The lacteals, 97 25. Blood corpuscles, 102 26. Blood corpuscles of man and lower animals, 103 27. Circulation of the blood, 108 {10} 28. Heart and large vessels, 109 29. Section of the heart, 110 30. Form of the pulse, 116 31. Valves of the veins, 117 32. Web of frog's foot, magnified, 119 33. Circulation in a frog's foot, 119 34. Organs of the chest, 124 35. Larynx, trachea, and bronchial tubes, 125 36. Diagram of the structure of the air-cells, 125 37. Section of the lungs, 126 38. Section of mouth and throat, 127 39. Ciliated cells, 128 40. Cerebro-spinal system, 151 41. Upper surface of the cerebrum, 153 42. Vertical section of the brain, 154 43. Base of the brain, 155 44. Brain and spinal cord, 156 45. Sense of touch, 185 46. Section of nasal cavity, 193 47. Front view of the eye, 200 48. Vertical section of eye, 202 49. Diagram for blind point of eye, 207 50. Retinal image, 210 51. Different shapes of the globe of the eye, 212 52. Function of accommodation, 214 53. Diagram of the ear, 218 54. Section of the ear, 221 55. Section of larynx and trachea, 229 56. View of vocal cords by the laryngoscope, 232 57. Different positions of vocal cords, 232 58. Simple microscope, 238 59. Compound microscope, 239 60. Household microscope, 240 61. Popular microscope, 241

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INTRODUCTION.

o------

The Human Body is the abode of an immortal spirit, and is the most complete and perfect specimen of the Creator's handiwork. To examine its structure, to ascertain the uses and modes of action of its various parts, how to protect it from injury, and maintain it in a healthy condition, is the design of this work.

The departments of knowledge which are concerned in these investigations, are the science of Human Physiology and the art of Hygiene.

PHYSIOLOGY treats of the vital actions and uses of the various parts of living bodies, whether vegetable or animal. Every living thing, therefore, has a Physiology. We have a _Vegetable_ Physiology, which relates to plants; and an _Animal_ Physiology, relating to the animal kingdom. The latter is also divided into _Comparative_ Physiology, which treats of the inferior races of animals, and _Human_ Physiology, which teaches the uses of the various parts of the human body.

HYGIENE, or the art of preserving health, is the practical use of Physiology. It teaches us how to cultivate our bodily and mental powers, so as to increase our strength and to fit us for a higher enjoyment of life. It also shows us how to prevent some of the accidents which may befall the body, and to avoid disease. It is proper that we should {12} understand the construction and powers of our bodies; but it is our duty, as rational beings, to know the laws by which health and strength may be maintained and disease warded off.

There are various means by which we gain important information respecting the Physiology of man. Plants aid us in understanding the minute structure of the human body, its circulation, and absorption. From inferior animals we learn much in respect to the workings of the different _organs_, as we call those parts of the system which have a particular duty to perform. In one of them, as in the foot of the frog, we can study the circulation of the blood; in another, we can study the action of the brain.

By _vivisection_, or the laying bare of some organ of a living animal, we are able to investigate certain vital processes which are too deeply hidden in the human body to be studied directly. This is not necessarily a cruel procedure, as we can, by the use of anæsthetics, so blunt the sensibility of the animal under operation, that he need not suffer while the experiment is being performed. There are other means by which we gather our information. There are occasionally men, who, from some accident, present certain parts, naturally out of view, in exposed positions. In these cases, our knowledge is of much greater value than when obtained from creatures lower in the scale of being than man.

We are greatly aided, also, by the use of various instruments of modern invention. Chief among these is the microscope, which is, as we shall learn hereafter, an arrangement and combination of lenses in such a way as greatly to magnify the objects we wish to examine. {13}

We have much to say of Life, or vital activity, in the course of our study of Physiology; but the most that we know of it is seen in its results. What Life is, or where its precise position is, we are not able to determine. We discover one thing, however, that all the parts of the body are united together with wonderful sympathy, so that one part cannot be injured and other parts not suffer damage. It is further evident that all organs are not equally important in carrying on the work of Life; for some may temporarily suspend their action, without serious results to the system, while others must never cease from acting. Yet there is nothing superfluous or without aim in our frames, and no part or organ can suffer harm without actual loss to the general bodily health. On this point Science and Holy Writ strictly agree.

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PHYSIOLOGY,

AND

HYGIENE.