THE INFLUENCE OF LIGHT ON LIFE 249 



to quality and quantity, to literally use light beneficially in the 

 treatment of the Insane. That coloured light should have any 

 effect at all may perhaps appear a little strange until enquired into. 



Without entering into the question of the wave-lengths and 

 degrees of refrangibility of the different colour-rays of the spectrum, 

 it will be sufficient to call attention to one or two examples of the 

 influence of coloured light. Turkeys are irritated by red and bulls 

 also, a fact which gladiators take advantage of, we are told, when 

 they wish to excite to rage the bulls with which they are to combat. 

 If, then, red excites some animals, why should not some other 

 colour soothe them ? In the treatment of the Insane, just men- 

 tioned, red is recognised as an exciting colour, blue and violet as 

 saddening ones, and green as a soothing one. 



Prof. Semper informs us that under green light frogs disengage 

 more carbonic acid than under a red light; and that under a green 

 Hght tadpoles will not develop into frogs ; while white rabbits are 

 said to be most certainly and easily reared in a white reflected 

 light. Sir John Lubbock found that Water-Fleas (Daphnia) pre- 

 ferred yellow or green light to white light, and in his book on Ants 

 and Bees he quotes a great many experiments which he had made 

 with the view of ascertaining which colours were most preferred 

 by ants. We cannot here quote the different results he obtained 

 under varying conditions, but we can relate one of the experiments. 

 He covered the box which contained the ants with strips of 

 coloured glass — green, yellow, red, and violet — and then counted 

 the number of ants which took up their position under the various 

 colours. After half-an-hour he changed the position of the glass 

 slips, putting the red where the green was before, and so on, and 

 the ants then re-arranged themselves. In twelve experiments it 

 was found that the total number which stayed under the red glass 

 was 890, under the green 544, under the yellow 495, and under 

 the violet only 5. Although the violet glass was as dark in shade 

 as the red, and darker than the green, yet it is remarkable that the 

 ants had a decided objection to the violet light. As a rule. Sir 

 John found that the ants collected in the shadiest place in the box, 

 but they did not prefer the shade of violet glass, although it was 

 much more shady to our eyes than the green or yellow glass. 



International Journal of Microscopy and Natural Science. 



Third Series. Vol V. s 



