242 THE INFLUENCE OF LIGHT ON LIFE. 



When we refer to the greatest influence for good which light 

 exerts on plant life, we are almost naturally led to ask, Is it pos- 

 sible that light also exerts an influence on animal life ? And if so, 

 surely there must also be in that kingdom a certain measure of the 

 subtle influence which also proves most beneficial. 



Such a consideration, then, forms the second part of our paper. 

 We have just seen that light is essential to the very life of a plant, 

 but it can scarcely be said in exactly the same way that light is 

 absolutely essential to the existence of all animals. It is true that 

 animals are altogether dependent upon plants, either directly or 

 indirectly, for the supply of food, and, as plants are altogether 

 dependent on light, therefore animals could not exist without hght, 

 but, putting that indirect dependence to one side, we do not find 

 that the total withdrawal of light is always followed by the death 

 of the creature in the same way as we found that the total with- 

 drawal was the death of the plant. 



In animals we have no chlorophyll to deal with, qxcqy>^ perhaps 

 in a few instances, such as Hydfa vtfidis, Euglena, and Stentor; 

 and, therefore, if we find hght agreeable or necessary to the life of 

 an animal, it must be for some other reason than that for which a 

 plant requires it. In Professor Semper's book on Animal Life 

 (International Scientific Series), he goes so far as to suggest that 

 animals may be at least as dependent as plants on the direct influ- 

 ence of light, although the nature of the relation may be altogether 

 different. I daresay that most of us have read the story regarding 

 Van Helmont, a celebrated alchemist doctor in the time of Louis 

 XIV., and the wonderful power which he attributed to the rays of 

 the sun. " Scoop out," he wrote, " a hole in a brick ; put into it 

 sweet basil, crushed; lay a second brick upon the first, so that the 

 hole may be perfectly covered. Expose the two bricks to the sun. 

 and at the end of a few days the smell of the sweet basil, acting 

 as a ferment, wiU change the herb into real scorpions." Present- 

 day science scarcely ascribes such an influence as that to the sun's 

 light ; but it certainly does present us with many wonderful results, 

 and results which I daresay would have surprised Van Helmont 

 quite as much as his production of scorpions surprises us. 



Dr. Carpenter, in his Physiology^ states that if cockroaches are 

 reared in an entire absence of fight, they will grow all right, but 



