314 THE CAUSES OF THE xi 



details of which chemists do not yet understand, 

 though they are near foreshadowing them, it 

 combines them into one substance, which is known 

 to us as " Protein," a complex compound of carbon, 

 hydrogen, oxygen, and nitrogen, which alone pos- 

 sesses the property of manifesting vitality and of 

 permanently supporting animal life. So that, you 

 see, the waste products of the animal economy, 

 the effete materials which are continually being 

 thrown off by all living beings, in the form of 

 organic matters, are constantly replaced by sup- 

 plies of the necessary repairing and rebuilding 

 materials drawn from the plants, which in their 

 turn manufacture them, so to speak, by a 

 mysterious combination of those same inorganic 

 materials. 



Let us trace out the history of the horse in 

 another direction. After a certain time, as the 

 result of sickness or disease, the effect of accident, 

 or the consequence of old age, sooner or later, the 

 animal dies. The multitudinous operations of 

 this beautiful mechanism flag in their perform- 

 ance, the horse loses its vigour, and after passing 

 through the curious series of changes comprised 

 in its formation and preservation, it finally decays, 

 and ends its life by going back into that inorganic 

 world from which all but an inappreciable fraction 

 of its substance was derived. Its bones become 

 mere carbonate and phosphate of lime \ the matter 

 of its flesh, and of its other parts, becomes, in the 



