PHYSIOLOGY. 
BOOK IT. 
some plants will grow in an atmosphere of hydrogen, while 
others quickly perish under such treatment. 
Drs. Turner and Cliristison found that so small a quantity 
as ^^-^ of sulphurous acid gas, — a proportion so minute as 
to be imperceptible to the smell, — was sufficient to destroy 
the life of leaves in forty-eight hours. The same observers 
state, in an excellent paper in Brewster's Journal for January, 
1828, the effects of other gases upon plants. I much regret 
that want of space prevents my giving their experiments in 
detail : the results, which are as follows, are very important. 
Hydrochloric or muriatic acid gas was found to produce 
effects not inferior, — nay, even superior, — to those of the 
sulphurous acid. It was found that so small a quantity as a 
fifth of an inch, although diluted with 10,000 parts of air, 
destroyed the whole vegetation of a plant of considerable size 
in less than two days. " Nay, we afterwards found that a 
tenth part of a cubic inch in 20,000 volumes of air had nearly 
the same effects. In twenty-four hours the leaves of a labur- 
num were all curled in on the edges, dry and discoloured; 
and, though it was then removed into the air, they gradually 
shrivelled and died. Like the sulphurous acid, the hydro- 
chloric acid gas acts thus injuriously in a proportion which is 
not perceptible to the smell. Even a thousandth part of 
hydrochloric acid gas is not distinctly perceptible ; a ten- 
thousandth made no impression on the nostrils whatever, 
although great care was taken to dry thoroughly the vessels 
used in making the mixtures." 
" Chlorine may be expected to have the effects of hydro- 
chloric acid gas ; and so indeed it has, but they appear to be 
developed more slowly. Two cubic inches in two hundred 
parts of air did not begin to affect a mignonette plant for three 
hours ; half a cubic inch in a thousand parts of air did not 
injure another in twenty-four hours : but when the plants did 
become affected, the same drooping, bleaching, and desiccation 
were observed." 
" Nitrous acid gas is probably as deleterious as the sul- 
phurous and hydrochloric acid gases. In the proportion of a 
hundred and eightieth, it attacked the leaves of a mignionette 
plant in ten minutes; and half a cubic inch in 700 volumes of 
