THE EXTENSION OF THE PRINCIPLE. 118 
proverb. I have already mentioned the effects of 
light upon vegetation ; and its influence upon the 
animal economy, although not so immediately 
obvious, is not the less striking. Milne-Edwards 
tells us, that if tadpoles be nourished with proper 
food, and are exposed to the constantly renewed 
action of water (so that their branchial respiration 
be maintained) but are entirely deprived of light, 
their growth continues, but their change into the 
condition of air-breathing animals is arrested, and 
they remain in the form of large tadpoles. Dr. 
Edwards also observes, that persons who live in 
caves and cellars, or in very dark and narrow 
streets, are apt to produce deformed children ; and 
that men who work in mines are liable to disease 
and deformity beyond what the simple closeness 
of the atmosphere would be likely to produce. 
Mr. Watson, of the Deaf and Dumb Asylum, 
informed me that, cceteris paribus , more deaf and 
dumb children were born in dark than in light 
dwellings. Sir James Wylie stated, some years 
ago, that the cases of disease in the dark side of 
an extensive barrack at St. Petersburg, have 
been uniformly, for many years, in the propor- 
tion of three to one of those on the side exposed 
to strong light. 
The more the body is exposed to the influence 
of strong light, the more freedom do we find, 
