190 NATURE AND LIFE. 
beautiful arum is found in our woods, the cuckoo-pintle, 
whose white flower diffuses a disgusting odor. Now, the 
inside of this flower is often filled with flies, snails, and 
plant-lice, seeking the putrid source of this fetid smell. We 
may see the little creatures, in quest of their food or of a fit 
place to lay their eggs, move about in all directions, and quit 
most unwillingly the flower whose scent has misled them. 
Il. 
Having thus learned what physiologists think of the 
sense of smell and the conditions of the perception of odors, 
let us see what naturalists and chemists have ascertained 
respecting the latter as viewed in themselves; what place 
they give to odorous bodies, and what character they at- 
tribute to them all. The three kingdoms possess odors. 
Among mineral substances, few solids, but quite a number 
of liquids and gases, are endowed with more or less power- 
ful scents, in most cases not very pleasant ones, and usually 
characteristic. Those odors belong to simple substances, 
such as chlorine, bromine, and iodine ; to acids, as hydro- 
chloric and hydrocyanic acid ; to carburets of hydrogen, as 
those of petroleum; to alkaline substances, ammonia, for 
instance, etc. The odors observable among minerals may 
almost all be referred either to hydrocarbonic or hydrosul- 
phuric gases, or to various solid and liquid acids produced 
by the decomposition of fats, or to peculiar principles se- 
ereted by glands, such as musk, ambergris, civet, and the 
like. Vegetables present quite another variety of odors, 
from the faintest to the rankest, from the most delicious to 
the most disgusting. Absolutely scentless plants are very 
rare, and many, that seem to be so while they are fresh, 
gain, on drying, a very decided perfume. 
The odor of plants is due to principles very unequally 
distributed throughout their different organs; some solid, 
as resins and balsams ; others which are liquid, and known 

