24 STUDIES IN LIFE AND SENSE. 



so Dame Nature contrives a use for the waste carbonic acid of the 

 animal world. She introduces the green plants on the scene as her 

 helpmates and allies in the economical work. Every green leaf we 

 see, is essentially a devourer of carbonic acid gas from the atmo- 

 sphere. That which the animal gives out, the green plant takes in. 

 Not so your mushrooms and other grovellers of the vegetable king- 

 dom, which, having no green about them, refuse to accept the cast- 

 off products of the animal series, and despise the carbonic acid as a 

 poor but proud relation discards the gift of our old garments. The 

 green plant is the recipient of the animal waste. The leaves drink 

 in the carbonic acid which has been exhaled into the atmosphere by 

 the tribes of animals. They receive it into their microscopic cells, 

 each of which, with its living protoplasm and its chlorophyll or green 

 granules, is really a little chemical laboratory devoted to the utilisa- 

 tion of waste products. Therein, the carbonic acid gas is received ; 

 therein, it is dexterously split up, " decomposed," as chemists wouki 

 have it, into its original elements, carbon and oxygen ; and therein 

 is the carbon retained as part of the food of the plant, while the 

 oxygen, liberated from its carbon bonds, is allowed to escape back 

 into the atmosphere to become once again useful for the purposes 

 of animal life. 



There would thus appear to be a continual interchange taking 

 place between the animal and plant worlds a perpetual utilisation 

 by the latter of the waste products of the former. It is immaterial 

 to this main point in natural economics that the reception of carbonic 

 acid by green plants can only proceed in the presence of light. It is 

 equally immaterial that by night these green plants become like 

 animals, and receive oxygen (an action which, by the way, they also 

 exhibit by day) and emit carbonic acid. These facts do not affect 

 the main point at issue, which is the direct use by the plant of 

 animal waste, and a very pretty cycle of operations would thus appear 

 to have been established when botanical research showed the inter- 

 actions to which we have just alluded. 



Going a step further in the same direction, we may find that this 

 utilisation of animal waste is by no means limited to the mere recep- 

 tion and decomposition of carbonic acid gas by green plants. It 

 may be shown that the economical routine of Nature is illustrated in 

 other phases of the common life of the world. The general food of 

 plants is really animal waste. We fructify our fields and gardens 

 with the excretions of the animal world. The ammonia which plants 

 demand for food is supplied by the decay of living material, largely 

 animal in its nature ; and even the sordid fungi flourish amid decay, 

 and use up in the system of natural economy many products for 

 which it would be hard or impossible to find any other use. What 

 we, in ordinary language, term "putrefaction" or " decay," is really a 



