CHAP. XII. 
RESPIRATION. 
387 
began in a few minutes ; and if the quantity was not great, 
the parts not attacked generally survived, if the plants were 
removed into the air. The sulphuretted hydrogen acts dif- 
ferently ; two cubic inches, in 230 times their volume of air, 
had no effect in twenty-four hours. Four inches and a half, in 
eighty volumes of air, caused no injury in twelve hours; but, 
in twenty-four hours, several of the leaves, without being 
injured in colour, were hanging down perpendicularly from 
the leafstalks, and quite flaccid ; and, though the plant was 
then removed into the open air, the stem itself soon began 
also to droop and bend, and the whole plant speedily fell over 
and died. When the effects of a large quantity, such as six 
inches in sixty times their volume, were carefully watched, it 
was remarked that the drooping began in ten hours, at once 
from the leafstalks ; and the leaves themselves, except that 
they were flaccid, did not look unhealthy. Not one plant 
recovered, any of whose leaves had drooped before it was 
removed into the air. 
“ The effects of ammonia were precisely similar to those of 
sulphuretted hydrogen just related, except that after the leaves 
drooped they became also somewhat shrivelled. The pro- 
gressive flaccidity of the leaves ; the bending of them at their 
point of junction with the footstalk, and the subsequent bend- 
ing of the stem ; the creeping, as it were, of the languor and 
exhaustion from leaf to leaf, and then down the stem, were 
very striking. Two inches of gas, in 230 volumes of air, 
began to operate in ten hours. A larger quantity and pro- 
portion seemed to operate more slowly. 
“ Cyanogen appears allied to the two last gases in property, 
but is more energetic. Two cubic inches, diluted with 230 
times their volume of air, affected a mignonette plant in five 
hours ; half a cubic inch, in 700 volumes of air, affected another 
in twelve hours ; and a third of a cubic inch, in 1700 volumes 
of air, affected another in twenty-four hours. The leaves 
drooped from the stem without losing colour ; and removal 
into the air, after the drooping began, did not save the plants. 
Carbonic oxide is also probably of the same class, but its 
power is much inferior. Four cubic inches and a half, diluted 
with 100 times their volume of air, had no effect in twenty- 
c c 2 
