LIGHT AND LIFE. 



33 



concludes that artificial light is impotent to do what solar light can. 

 The labors of Prillieux and other contemporary botanists have proved 

 that all light acts on the respiration of plants, provided only it is not 

 too powerful. In Biot's case artificial light had no effect, because it 

 it was far too intense. 



III. 



Lavoisier somewhere says : " Organization, voluntary movement, 

 life, exist only at the surface of the earth, in places exposed to light. 

 One might say that the fable of Pi'ometheus's torch was the expression 

 of a philosophic truth that the ancients had not overlooked. Without 

 light, Nature was without life ; she was inanimate and dead. A be- 

 nevolent God, bringing light, diffused over the earth's surface organi- 

 zation, feeling, and thought." These words are essentially true. All 

 organic activity was very clearly at first borrowed from the sun, and if 

 the earth has since stored away and made its own a quantity of energy, 

 that sometimes suffices to produce of itself that which originally pro- 

 ceeded from solar stimulus, it must not be forgotten that those living 

 forces, of startling and complex aspects, sometimes our pitiless ene- 

 mies, often our docile servants, have descended, and are still descend- 

 ing upon our planet, from the inexhaustible sun. The study of animal 

 life shows us by striking instances the physiological efficacy of light, 

 and the immaterial chain, it may be called, which links existences with 

 the fiery and abounding heart of the known universe. 



In plants, as we have seen, respiration at night is the reverse of 

 that by day. There are infusoria which behave, under the influence 

 of light, exactly like the green portions of plants. These microscopic 

 animalcula are developed in fine weather in stagnant water, and in 

 breathing produce oxygen at the expense of the carbonic acid con- 

 tained in the liquid. Morren saw that the oxygenation of the water 

 occasioned by these little beings varied very perceptibly in the course 

 of twenty-four hours. It is at the minimum at sunrise, and reaches 

 its maximum toward four in the afternoon. If the sky is overcast, or 

 the animalcula disappear, the phenomenon is suspended. Tbis is only 

 an exception. Animals breathe at night in the same way as in the 

 daytime, only less energetically. Day and night they burn carbon 

 within their tissues, and form carbonic acid, only the activity of the 

 phenomenon is much greater in light than in darkness. 



Light quickens vital movements in animals, especially the act of 

 nutrition, and darkness checks them. This fact, long known and ap- 

 plied in practical agriculture, is expressly noted by Columella. He 

 recommends the process of fattening fowls by rearing them in small 

 dark cages. The laborer, to fatten his cattle, shuts them up in stables 

 lighted by small low windows. In the half-light of these prisons the 

 work of disassimilation goes on slowly, and the nutritive substances, 

 instead of. being consumed in the circulating fluid, more readily accu- 



