5 86 THE POPULAR SCIENCE MONTHLY. 



character of the different parts of which it is composed, but of the 

 relations of these parts to each other. The force operating such a 

 machine may be derived from a simple fall of water, or from the oxida- 

 tion of burning anthracite ; but, although this may be the sole source of 

 the actual energy expended, it is far from being the only factor con- 

 cerned in the production of the special kind of work accomplished. 

 The results are due to the transformations of this initial force into 

 force of other kinds, the character of the work done depending on the 

 peculiar construction of the machine in other words, on the relations 

 of its parts. Thus the expansive power of steam may be expended in 

 the idle clapping of the lid of a tea-kettle, or in the driving of the 

 piston in the engine of an ocean-steamer, according to the relations 

 into which the steam is brought. Keeping this illustration in mind, 

 we may perhaps attain to some conception of the meaning of a living 

 organism, and wherein consist the differences in different organisms. 



The life-processes are concerned in the building up of the tissues 

 that is, in the construction and constant repair of the mechanism out 

 of materials supplied by food ; coincident with this assimilation of 

 new material, there is a corresponding accumulation of energy or 

 force. The energies liberated, on the other hand, in the activities of 

 muscle, nerve, brain, etc., come from the oxidation the so-called 

 waste of these tissues ; and (as in the machine) the results produced 

 are due to the transformations of this initial force, derived from oxida- 

 tion of the tissues, into other kinds of force, viz., those manifested by 

 living animal organisms, the character of the work done depending (as 

 in the illustration) on the particular construction of the mechanism 

 concerned. In the operations of living organisms, not less than in 

 those mechanisms whose motive power is derived from steam, not a 

 known law of matter is violated, but all are wrought into a harmony 

 so complete that the entire complex and heterogeneous structure acts 

 as a unit. 



Glancing in thought over the vast expanse of matter of which the 

 universe consists, what has been the direction of the progress witnessed 

 through the long ages since the beginning condensation of the nebu- 

 lous masses in which our solar system is believed to have originated ? 

 The immense globes which whirl in repeated circles through the 

 heavenly spaces, though bound together by the strongest and most 

 subtile bonds, roll blindly on, forever unconscious of themselves and of 

 one another. The lily of the field even, clothed in beauty though it 

 be, and surrounded by the greater glories of earth and sky the warm 

 sunshine and green fields has no conscious enjoyment of itself or of 

 them ; but as elements identical with those which compose these 

 unconscious forms have combined and recombined in compounds of 

 increasing complexity, as molecules have condensed and differentiated 

 in the development of a higher kind of living matter, consciousness has 

 dawned, and (mainly through the avenues of the special senses) mind 



