158 Professor G. V. Poore [April 24^ 



panied by nitrogen, sulphuric acid and volatile hydrocarbons. The 

 residue consists mainly of silica and alumina, which are removed from 

 the furnace in the form of clinker and ash. The water ultimately 

 returns to the earth in the form of rain or dew, the carbonic acid is 

 ultimately absorbed by green plants, and, by stimulating the growth 

 of these, helps to furnish us with more combustible material, while 

 the residue is almost a waste product. Thus, in this example we find 

 that the carbon and watery vapour readily " cireulate,^^ while the 

 residue can only do so after a long interval of time, and is practically 

 lost. The volatile hydrocarbons and sulphuric acid, being poisonous 

 to herbage, are a source of practical loss rather than gain. 



Let us take next the case of an animal, which is really a living^ 

 furnace, browsing in a field ; as it browses we may often see the 

 breath, which is the smoke of this furnace laden with carbonic acid 

 and water, escaping from its mouth and nostrils, and it is probable 

 that the green leaves of the herbage absorb this carbonic acid almost 

 as soon as it escapes, and, appropriating the carbon, return oxygen to 

 the animal to help its respiration and combustion. The animal as it 

 eats continues to grow and increase in bulk and value, whereas the 

 artificial furnace in which the coal is burnt tends steadily to wear 

 out and decrease in value. As it browses and grows, the droppings of 

 the animal nourish the herbage which here and there, by patches of 

 more vigorous growth and deeper green, aflbrd sure evidence of the 

 value of these waste products. 



In this arrangement there is no waste, for both the animal and 

 the herbage, by a process of mutual exchange and the circulation of 

 organic matter, increase in value. 



Not only is there no waste, but, strange as it may seem, there is a 

 positive gain, with no loss whatever. The furnace and the fuel are 

 both increased ! This increase can only be apparent, and not real, 

 for it is well known that although we may alter the form of matter, 

 we can add nothing to and subtract nothing from the sum total of 

 the world. 



One would say that this apparent increase is due to the stimulat- 

 ing effect of the excreta upon the soil, which enables us to draw 

 something extra from that inexhaustible storehouse of plant-food and 

 water, and enables the animal to use these materials, instead of allow- 

 ing them to drain to the springs, and so find their way to the sea. 

 We know that a far greater proportion of the rainfall percolates 

 through barren soil than through soil bearing crops. If this be so, 

 there is a practical increase of the land at the expense of the water. 



Again, we must remember that our knowledge of the sources of 

 the gases of the atmosphere is not complete. It may be that all the 

 oxygen of the air is furnished by the green leaves of plants, and all 

 the carbonic acid by processes of respiration and combustion, but we 

 are by no means sure of this. Of the sources of the atmospheric 

 nitrogen we know nothing. Now it is certain that much of the carbon 

 of the atmosphere is appropriated by the plants, and much of the 



