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of Edinburgh, Session 1866 - 67 . 
observation, and asserting the vast importance of the subject in its 
social aspects, we venture to say that science furnishes us with 
principles and methods by which the light of day may be thrown 
into apartments which a sunbeam has never reached, and where the 
poisons and the malaria of darkness have been undermining sound 
constitutions, and carrying thousands prematurely to the grave. 
The influence of light upon vegetable life has been long and suc- 
cessfully studied by the chemist and the botanist. The researches 
of Priestley, Ingenhousz, Sennehier, and Decandolle, and the more 
recent ones of Carradori, Payen, Macaire, Draper, Gratiolet, 
Gardner, Daubeny, and Hunt, have placed it beyohd a doubt that 
sunlight exerts the most marked influence upon the respiration, 
the absorption, and the exhalation of plants, and, consequently, 
on their general and local nutrition. Draper and Gardner deter- 
mined the influence of the differently coloured rays in the germi- 
nation of plants and in the decomposition of carbonic acid, and they 
found that the yellow rays were particularly active in producing the 
green colour of the leaves. Mr Hunt has shown that the germination 
of seeds is more rapid under the influence of the chemical rays than 
in the dark or even under white light — a result confirmed by the 
observations, on a large scale, of the Messrs Lawson and Sons. 
The curious fact of plants bending towards the light, as if to catch 
its influence, must have been frequently observed. Mr Hunt found 
that this influence, which is strikingly shown by the potato, is due 
to the action of the yellow rays , and, what is very remarkable, 
that in red light the plant bends from it. 
If light, then, is so essential to the life of plants, we may reason- 
ably suppose that it is necessary, though to a less extent, to the 
development and growth of animals ; and many observations have 
been recently made in confirmation of this important fact. Dr 
Edwards found that all the eggs of frogs exposed to light were 
developed in succession, but that none of those kept in the dark 
were well developed. Employing the tadpoles of the Rana obstetri- 
cansy he found that the action of light developes the different parts 
of the body in that just proportion which characterises the adult 
— the type of the species. 
In papers communicated to the Imperial Academy of Sciences, 
M. Moleschoff of Heidelberg has shown that the quantity of car- 
