CHAPTER I. 



ANIAIAL STRUCTURE AND FUNCTION. 



A KNOWLEDGE of the Structure of the various parts of the body 

 {aiiato7ny) and the functions they performi {physiology)^ provides a 

 rational foundation on which to base our acquaintance with animals, 

 their requirements and capabilities ; and so that all may get a clear idea 

 of these complex and technical subjects, necessary references to them 

 are given in as simple language as possible. 



Cells. — All animal bodies are composed of cells. A cell is a minute Cells, 

 round mass of living matter, which may or may not possess the property of 

 moving itself. Though at first all cells appear alike, they soon become 

 specialised to perform one particular duty, e.g.^ the liver cell makes bile ; 

 the muscle cell acquires the power of contraction. As they increase in 

 number, the pressure of surrounding cells causes them to alter in shape 

 and they may become many sided, flat or spindle-shaped. The entire 

 animal is made up of such minute, specialised bodies, a single cell 

 bearing the same relation to the whole body that a brick does to 

 London. Cells multiply by dividing, each portion attaining to the size 

 of its parent. This power is most marked in youth, growth^ and 

 declines in age, decay. 



Bones. — The framework of the body is constructed of bones^ so Bones, 

 arranged that they can be used as rigid supports, or become freely 

 movable when the joints are brought into play. A joint is formed joints, 

 wherever two bones meet and move over each other ; it is always 

 surrounded by an air-tight capsule, and in order to prevent any friction, 

 the ends of the bones are covered by thick layers of gristle {cartilage\ 

 which have extremely smooth surfaces. Inside the joint are found special 

 fringes which lie loosely in the capsule and produce "joint oil " {synovia), a 

 peculiarly oily, slippery fluid, which bathes the entire joint and ensures 

 the most perfect lubrication. The movement of joints is accompHshed 

 by the action of muscles. 



Muscles are the red butcher's meat which we eat, constitute a great Muscles, 

 part of the body, and are attached to the bones in such fashion as to 



