CHAPTER VI. 



ANIMAL STRUCTURE. 



PHYSIOLOGY HISTOLOGY — CELL THEORY — GROWTH OF TISSUES- 

 SPECIAL TISSUES SKIN, CARTILAGE, TEETH, BONE, ETC. 



>HE most complicated state in which matter ex- 

 ists, is where, under the influence of life, it 

 forms bodies with a curious internal struc- 

 ture of tubes and cavities, in which fluids 

 are moving and producing incessant internal 

 change," says the philosophic Dr. Arnott. 

 These are called organised bodies, because 

 of the various organs which they contain ; 

 and they form two remarkable classes ; th,e 

 individuals of one of which are fixed to the soil, and 

 are called vegetables, — of these we shall consider the 

 structure at a future stage ; the individuals of the 

 other are endowed with power of locomotion, and 

 are called animals : it is some of the peculiarities and 

 minute structure of this latter class that we are now 

 about to examine. The phenomena of growth, decay, death, sensation, 

 self-motion, and many others, belong to life ; but, from occurring all 

 in material structures, which subsist in obedience to the laws of phy- 

 sics and chemistry, the life is truly a superstructure on the other two, 

 and cannot be studied independently of them. Indeed, the greater 

 part of the phenomena of life are merely chemical and physical pheno- 

 mena, modified by an additional principle. The phenomena of life, 

 from thus involving generally the agency of all the sets of laws, are by 

 far the most complex of any ; and the discovery or detection of the 

 peculiar laws of life, although they are fixed as the laws of chemistry 

 or physics, has been very slow, and is as yet far from being completed. 

 The study of the Science of Life, or the building up of the living 



