5 



gent mind that this process could not go on forever without the 

 capacity of being repaired. 



We therefore have recourse to food to supply the waste. Broadly 

 speaking, the animal body is a machine well adapted for convert- 

 ing potential energy into actual energy. The potential energy is 

 supplied by the food we eat ; this the metabolism of the body con- 

 verts into kinetic or actual energy of heat and mechanical labor. 

 So we may say that our bodies are delicately constructed heat 

 engines. 



Energy, like matter, is indestructible and of two kinds— kinetic, 

 or actual, and potential, or positive energy. Our whole life con- 

 sists but in the transformation of these two different kinds of 

 energy. We procure food which we eat, the greater part of which, 

 undci chemical action of various juices of the digestive organs, is 

 absorbed into our system, which thereby enables us to perform a 

 certain amount of work, mental or physical ; in other words, to 

 transform a certain amount of potential into kinetic or actual 

 energy. For a certain amount of work to be done (without waste 

 or injury to the system), a certain amount of food must be ab- 

 sorbed, that is, digested. If the absorption be in excess of the 

 expenditure, then nature stores this energy up in the form of fat ; 

 if the expenditure be 'n excess of absorption, then nature works 

 upon our bodies and we grow thin. If the absorption equal the 

 exoenditure, then we are in a state of what the doctors term 

 physiological equilibrium, in perfect good health. 



Energy is expended in building organic substances, or, in other 

 words, in converting food stuffs of any kind into protoplasm, the 

 summit of the double stair of life, and its potential energy is the 

 transformed or stored energy of the above mentioned constructive 

 process. 



Man, like all animals, is born of an egg, or ovum, which was the 

 first germ of our existence, and is a small cell about one-hundredth 

 of an inch in diameter, consisting of a mass of semi-fluid proto- 

 plasm enclosed in a membrane, and containing a small speck or 

 nucleus of more condensed protoplasm. This nucleated cell is 

 itself the first fcrm into which a mass of sinlple jelly-like proto- 

 plasm is differentiated in the course of its evolution from its 

 original uniform composition. This nucleated cell is the starting 

 point of all higher life, and by splitting up and multiplying repe- 

 titions of itself in geometrical progression, provides the cell 

 material out of which all the more complicated structures of living 

 things are built up. At first the ^^,g behaves exactly as any other 

 single-celled organism, as, for instance, that of the ameba, which is 

 considered the simplest form of all organized life. One of the 

 simplest forms of this is nothing but a naked little lump of cell- 

 matter, or plasma, containing a nucleus ; and yet this little speck 

 of jelly moves freely. It shoots out tongues or processes and gradu- 

 ally draws itself up with a sort of wave-like motion ; it efits and 

 grows, and in growing reproduces itself by contracting in the- 

 middle and splitting up into independent ameba. 



