AN INVITATION TO DINNER. 353 



even the quiet moments of our lives are attended by and carried on 

 through work of a very severe character ; and this even when the 

 almost endless work of the brain in thought, and of the nerve-centres 

 in controlling the bodily actions, is entirely set aside and overlooked 

 in our calculation. 



Returning for a moment to Caudal, whom we left in the scales, 

 we may be required to specify the exact form in which the bodily 

 substance of the subject experimented upon has disappeared in the 

 acts and processes of life. Briefly stated, so much of our material 

 substance is given off from skin and lungs, for example, in the form 

 of water ; part is excreted in the shape of carbonic acid gas, which 

 thus becomes available as food for green plants ; and part of the wear 

 and tear is likewise given off in the form of heat, a curious substance 

 called " urea," and as ammonia and mineral matters. In other words, 

 our bodies, as the result of the work they perform, are perpetually 

 being dissipated into so much heat, water, carbonic acid gas, and 

 other substances. The animal frame is constantly breaking down into 

 these inorganic matters, and is thus at once finding a lower level of 

 existence and supplying the plant world with the matters from which 

 the life of the vegetable kingdom will evolve new growths and fresh 

 generations. Well might Erasmus Darwin write 



Hence, when a monarch or a mushroom dies, 

 Awhile extinct the organic matter lies, 

 But as a few short hours or years revolve, 

 Alchemic power the changing forms dissolve ; 

 Emerging matter from the grave returns, 

 Fills new desires, with new sensation burns. 



If it is true that " in the midst of life we are in death," it is no less 

 true that from the physiological charnel-house into which living beings 

 are perpetually doomed to pass, new forms take their origin. These 

 are fed by the matter which, having done duty in living bodies, is, 

 after a period of so-called decay, woven anew into the textures of 

 succeeding generations of animals and plants. 



The answer to the question with which we began our scientific 

 journeyings should now loom plainly enough ahead. We eat our 

 dinner because, in the food of which that meal consists, we expect 

 to find materials capable of replacing those we have lost in the 

 acts and processes of life. " Food," in this view, from dry bread to 

 Smith's choicest dainties, is only matter which the body demands 

 for its sustenance and support ; and the perfect diet is simply that 

 which affords us the most complete epitome of our bodily belongings 

 in most condensed form, and in a shape susceptible of ready 

 conversion, by digestion, into ourselves. We eat, then, because we 

 waste, and we waste because we work. There is no escape from 

 the continual wear and tear which besets us. We receive so much 



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