19. Hence the butcher's stall will furnish all the materials for the study of the microscopic tissues. The structure of the heart, lungs, liver, brain, and muscle may all be studied, and well studied, by using minute pieces of the flesh of the lower animals, especially of the quadrupeds. Such portions of these animals as are not exposed for sale can be readily obtained by order from the slaughter-house. To examine with the powers of which we have been speaking, it is only necessary to cut off {246} exceedingly small pieces, tear them apart with needles, or make very delicate sections with a sharp knife. 20. INCENTIVES TO STUDY.--A complete knowledge of all minute structures is not to be expected at once, for you are here introduced into a new realm of Nature, a world of little things as vast, as wonderful, and as carefully constructed as the starry firmament,--that other realm of grand objects which the astronomer nightly scans with the telescope. It will not appear singular, therefore, if, at first, you feel strange and awkward in this new creation. With a little perseverance, however, and with the attention directed toward simple objects at the outset, it will not be long before an increasing experience will engender confidence. 21. If to all this there be added an enthusiastic study of the standard authorities on the subject, the rate of progress will be by so much the more rapid. As compared with similar studies, few possess more interest than microscopy, and to the one who pursues it with fondness, it constantly affords sources of pleasure and agreeable surprises; and in the end, often leads to new and valuable additions to the sum of human knowledge. The depths which the microscope is employed to fathom are no more completely known, than are the heights above us explored and comprehended by the astronomer. QUESTIONS FOR TOPICAL REVIEW. _State what you can on the following subjects_: 1. Voice and speech 227, 228 2. The organ of the voice 228, 229 3. The vocal cords 230, 231 4. The production of the voice 232, 233 5. The varieties of voice 233, 234 6. Ventriloquism 235 7. The law of the tissues 236 8. Necessity of the microscope 236 9. Convex lenses 236, 237 10. Kinds of microscope 237, 238 11. Choosing a microscope 239, 242 12. Preliminary studies 243, 244 13. The study of human tissues 244 14. The study of the inferior animals 245 * * * * * {247} APPENDIX. ------o------ POISONS AND THEIR ANTIDOTES.