THE FARMER'S MAGAZINE. 



275 



parent vessel. All the eggs exposed to light were 

 developed in succession, but none of those in the 

 dark did well. 



As almost all animals are more or less exposed 

 to light after birth. Dr. Edwards thought it would 

 be interesting to determine the peculiar effect of 

 light upon the development of the body. As all 

 animals, in growing, gradually change their form 

 and proportions, and make it difficult to observe 

 slight shades of modification, he chose for his ex- 

 periments species among the vertebrata whose 

 development presents precise and palpable dif- 

 ferences. These conditions are combined in the 

 highest degree in the frog. In its first period it 

 has the form and even the mode of life of a fish, 

 with a tail and gills, and without limbs. In its 

 second period it is completely metamorphosed into 

 a reptile, having acquired four limbs, and lost its 

 tail and gills and all resemblance to a fish. Dr. 

 Edwards employed the tadpoles of the Rana 

 obstetricians, and he found that all those which 

 enjoyed the presence of the light underwent the 

 change of form appertaining to the adult. " We 

 see, then," says Dr. Edwards, " that the action of 

 light tends to develop the different j)arts of the 

 body in that just proportion which characterizes 

 the type of the species. This type is well cha- 

 racterized only in the adult. The deviations from 

 it are the more strongly marked the nearer the 

 animal is to the period of its birth. If, therefore, 

 there were any species existing in circumstances 

 unfavourable to their further development, they 

 might possibly long subsist under a type different 

 from that which nature had designed for them. 

 The Proteus anguiformis appears to be of this 

 number. The facts above mentioned tend to con- 

 firm this opinion. The Proteus anguiformis lives 

 in the subterraneous waters of Carniola, where the 

 absence of light unites with the low temperature 

 of those lakes in preventing the development of 

 the peculiar form of the adult. 



The experiments of M. Morren on the animal- 

 cules generated in stagnant waters, and those of 

 M. Moleshott on the respiration of frogs as mea- 

 sured by the quantity of carbonic acid gas which 

 they exhale, confirm the general results obtained 

 by Dr. Edwards ; but the most important re- 

 searches on the subject have just been published 

 by M. Beclard. During the last four years, he 

 has been occupied with a series of experiments on 

 the influence of the white and coloured light of 

 the spectrum, on the principal functions of nu- 

 trition ; and he has presented to the Academy of 

 Sciences, in a concise form, some of the more im- 

 portant results which he has obtained. 



Having placed the eggs of the fly (Musca car- 

 naria) in six bell glasses, violet, blue, red, yellow, 

 transparent, and green, he found, at the end of 

 four or five days, that the worms were most de- 

 veloped in the violet and blue glasses, and least in 

 green; the influence of the other colours diminishing 

 in the order we have named them from violet to 

 green. Between these extremes the worms de- 

 veloped were as three to one both with respect to 

 bulk and length. 



In studying the influence of the differently 

 coloured rays upon frogs, which have an energetic 



cutaneous respiration, equal and often superior to 

 their pulmonary respiration, M. Beclard found that 

 the same weight of frogs produced more than 

 twice the quantity of carbonic acid under the 

 green than under the red glass. When the same 

 frogs were skinned, the ojiposite result was ob- 

 tained. The carbonic acid was then greater in the 

 red than in the green rays. 



In a number of exjjeriments on the cutaneous 

 exhalations of the vapour of water from frogs, the 

 quantity was one-half less in darkness than in 

 ichite or violet light, in which the exhalation was 

 the same.* 



We come now to consider the influence of light 

 upon the human frame, physical and mental, in 

 health and disease, in developing the perfect form 

 of the adult, and in preserving it from premature 

 decay. We regret to find that our knowledge on 

 these points is so extremely limited, and we are 

 surprised that physicians and physiologists should 

 not have availed themselves of their numerous 

 opportunities, in hospitals, prisons, and mad- 

 houses, of studying so important a subject. AVe 

 must grope our way, therefore, among general 

 speculations and insulated facts, in the hope of 

 arriving at some positive rerults ; and we have no 

 doubt that the direct influence of light over the 

 phenomena of life will not be found limited to the 

 vegetable kingdom and the lower races of the 

 animal world. 



Man in his most perfect type is doubtless to be 

 found in the temperate regions of the globe, where 

 the solar influences of light, heat, and chemical 

 rays are so nicely balanced. Under the scorching 

 heat of the tropics, man cannot call into exercise 

 his higliest powers. The calorific rays are all- 

 powerful there, and lassitude of body and imma- 

 turity of mind are its necessary results ; while in 

 the darkness of the polar regions the distinctive 

 characters of our species almost disappear, in the 

 absence of those solar influences which are so 

 powerful in the organic world. 



It is well known to all who are obliged to seek 

 for health in a southern climate, that an ample 

 share of fight is considered necessary for its reco- 

 very. In all the hotels and lodging-houses in 

 France and Italy, the apartments with a south ex- 

 posure are earnestly sought for; and the patient, 

 under the advice of his physician, strives to fix 

 himself in these genial localities. The salutary 

 eflfect, however, thus ascribed to hght, might arise 

 from the greater warmth which accompanies the 

 solar rays ; but this can hardly be the case in mild 

 climates, or, indeed, in any climate where a fixed 



* " Professor E. Forbes and Mr. Couch have 

 both remarked that the vegetables and animals 

 near the surface of the sea are brilliantly coloured, 

 but that they gradually lose the brightness of their 

 hue as they descend, until the animals of the lowest 

 zone are found to be nearly colourless. . . . Or- 

 ganization and life exist only at the surface of our 

 planet, and under the influence of light. Those 

 depths of the ocean at which an everlasting dark- 

 ness prevail is the region of silence and eternal 

 death."— Hunt's Researches, S,-c., Appendix Noi 

 vii., p. 386. 



