486 CHEMISTRY IN AGRICULTURE AND PHYSIOLOGY. 
continually received, being deposited, in place of the old 
ones, which then constitute matters no longer available for 
the purpose of nutrition. And here again we see the won¬ 
derful provisions of nature in removing such from the sys¬ 
tem when they are no longer required. 
We have stated repeatedly, that the various carbonaceous 
matters unite with the oxygen taken in by the arterial blood, 
and are carried to the lungs and excreted with other portions 
of effete materials. From the decomposition of albumen, are 
taken elements to the liver to form bile, and lastly, the kidneys 
have for their office the removal of a large proportion of them 
in the form of urea, the quantities of course being dependent 
on the amount of waste; and here we observe a striking 
instance of the metamorphoses of the various tissues. 
If a person undergoes much bodily exertion, the amount of 
urea is increased; if, on the other hand, his employment has 
been that in which the assistance of the mind has been most 
active, the preponderance of phosphates will be evident, thus 
proving that even a thought is sufficient to make a call upon 
the sources of nutrition, so as to cause a partial destruction 
of the brain itself. Nevertheless we do not find that the mind 
decreases in power the more it is employed; on the contrary, 
it becomes more powerful the more it is exercised. Diffi¬ 
culties, which at first sight appear insurmountable, by careful 
investigation are often proved to be most simple. 
Thus step by step the mind proceeds, acquiring new 
strength and new capacity with every exertion; grasping 
Nature’s deepest mysteries, and seeking for the laws that 
govern them, uncoiling their most intricate windings with 
indefatigable perseverance, clearing away the mass of igno¬ 
rance and superstition which surrounds them, and making 
those facts which were hidden in depths almost unfathomable 
to appear clear and evident as the mid-day sun. 
Thus does education change the face of Nature, rendering 
that a fair plantation, which without it would appear a (i desert 
wild.” Well may we say with Pope: 
“ A little learning is a dangerous thing, 
- Drink deep or taste not the Pierian spring; 
Its shallow draughts intoxicate the brain, 
But drinking deeply sobers us again.” 
Thus we have seen that the functions of vitality are carried 
on to a certain duration, and then comes the cessation of 
nutrition and death. The once-moving body is now a motion¬ 
less mass, on w hich the laws of chemistry will soon exert 
their potent influence, converting the complicated animal 
organism into a number of noxious compounds, but even these 
