INTRODUCTORY. 11 



bility, it indicates to the system the state of the atmosphere 

 and other surrounding conditions, and gives warning of de- 

 structive influences. In some parts, as in the fingers, this 

 sensibility is most delicate and acute. Here the nerves of 

 sense are more closely distributed, and are in freer communi- 

 cation with each other. They act as sentinels to warn the 

 body of danger, and when danger is at hand they telegraph 

 to the brain or spinal cord to move the limb or body from 

 this exposed position, or to assume a position of defence. 

 The lightning speed with which these communications are 

 made may be seen when a finger unexpectedly comes in con- 

 tact with a hot substance. 



8. The Brain and Spinal Cord. We have now before 

 us a self-moving structure, made up of bones, ligaments to 

 hold together the bones at the joints, muscles, fat, connective 

 tissue and skin, with a nervous system, consisting of the 

 brain, spinal marrow, and nerves communicating with every 

 part, to superintend and manage this movable tenement. 

 The force required to move the system and the heat necessary 

 for life are self -created. 



9. Atoms. The body formed of these several tissues is 

 composed of material of limited durability. There is a limit 

 to life with regard to our individual being, but there -is a 

 much briefer limit to the life of the particles out of which the 

 tissues are constructed. Each of these atoms or cells has 

 an individual life. It passes a state of existence of com- 

 paratively short duration. During its term of existence it 

 has the ordinary stages of life birth, growth, development, 

 maturity, decline and death. The cells are the offspring of 

 parent cells, and in turn beget offspring before they die. In 

 infancy, childhood, maturity and old age the body is ever 

 perishing. It is this constant loss of particles, this wear and 

 tear of tissue, which causes the demand for daily food. Until 

 the body is fully matured, food is required for the growth of 



