15. What is said of disease? 16. Why is the study of physiology and hygiene important? -=-=-=-=-=-=-=-=-=-=-=-= CHAPTER II. STRUCTURE OF MAN, 17. In the structure of the human body, there is a union of fluids and solids. These are essentially the same, for the one is readily changed into the other. There is no fluid that does not contain solid matter in solution, and no solid matter that is destitute of fluid. 18. In different individuals, and at different periods of life the proportion of fluids and solids varies. In youth, the fluids are more abundant than in advanced life. For this reason, the limbs in childhood are soft and round, while in old age they assume a hard and wrinkled appearance. 19. The fluids not only contain the materials from which every part of the body is formed, but they are the medium for conveying the waste, decayed particles of matter from the system. They have various names, according to their nature and function; as, the blood, and the bile. 20. The solids are formed from the fluids, and consequently they are reduced, by chemical analysis, to the same ultimate elements. The particles of matter in solids are arranged variously; sometimes in _fi´bres_, (threads,) sometimes in _lam´i-næ_, (plates,) sometimes homogeneously, as in basement membranes. (Appendix A.) 21. The parts of the body are arranged into _Fi´bres_, _Fas-cic´u-li_, _Tis´sues_, _Or´gans_, _Ap-pa-ra´tus-es_, and _Sys´tems_. -=-=-=-=-=-=-=-=-=-=-=-= 17. What substances enter into the structure of the human body? Are they essentially the same? 18. What is said of these substances at different periods of life? 19. What offices do the fluids of the system perform? 20. What is said of the solids? How are the particles of matter arranged in solids? 21. Give an arrangement of the parts of the body. -=-=-=-=-=-=-=-=-=-=-=-= 22. A FIBRE is a thread of exceeding fineness. It is either cylindriform or flattened. 23. A FASCICULUS is the term applied to several fibres united. Its general characteristics are the same as fibres. 24. A TISSUE is a term applied to several different solids of the body. 25. An ORGAN is composed of tissues so arranged as to form an instrument designed for action. The action of an organ is called its _function_, or use. _Example._ The liver is an organ, and the secretion of the bile from the blood is one of its functions.[1] [1] Where examples and observations are given or experiments suggested, let the pupil mention other analogous ones. 26. An APPARATUS is an assemblage of organs designed to produce certain results. _Example._ The digestive apparatus consists of the teeth, stomach, liver, &c., all of which aid in the digestion of food. [Illustration: Fig. 2. Represents a portion of broken muscular fibre of animal life, (magnified about seven hundred diameters.)]