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 morganie 
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 
