VELLEIA. 
a portion of the descending sap enters. The 
substance of these roots, like that of the slender 
horizontal branches, is much less succulent than 
that of the radicle first emitted, and they are, in 
consequence, less obedient to gravitation; and 
therefore, meeting less resistance from the super- 
ficial soil than from that beneath it, they extend 
horizontally in every direction, growing with 
most rapidity, and producing the greatest num- 
ber of ramifications, wherever they find most 
warmth, and a soil best adapted. As these hori- 
zontal or lateral roots surround the base of the 
tree on every side, the true sap, descending down 
its bark, enters almost exclusively into them ; 
and the first perpendicular root, having executed 
its office of securing moisture to the plants whilst 
young, is thus deprived of proper nourishment, 
and, ceasing almost wholly to grow, becomes of 
no importance to the tree.” 
VEGETATION. See Vucurasiz PrysioLoey. 
VEGETO-ALKALIEKS. See Ankatorps. 
VELLA. See Cruss-Rocxer. 
VELLEIA. A genus of ornamental exotic 
plants, of the goodenia family. Three species, 
all yellow-flowered, evergreen herbs of between 
3 and 8 inches in height, have been introduced 
to British greenhouses from Australia; and some 
other species are known. 
VELLING. Ploughing up or paring the turf 
or surface of the ground preparatorily to its being 
burnt. 
VELTHEIMIA. A genus of ornamental, tu- 
berous-rooted, South-African plants, of the day- 
lily family. Three species, the green-leaved, the 
glaucous, and the intermediate, all about two 
feet high, and carrying light flesh-coloured flow- 
ers at an early period in spring, have been in- 
troduced to the greenhouses of Britain; and 
they love a soil of rich mould, and are propa- 
gated from offsets. 
VENISON. The flesh of deer. 
cles Drzr and Mrar. 
VENTILATION. ‘The frequent or constant 
circulation of pure air in confined apartments, 
occupied by man, by the lower animals, or by 
living plants, in sufficient quantity to prevent 
the accumulation of noxious gases. The neces- 
sity and principles of it are widely different in 
the case of animals and in that of plants; but 
they are the same in the case of man and in that 
of the domesticated animals,—the same for hu- 
man dwellings and for stables and cattle-houses ; 
and while we shall illustrate them in two sets, 
the one applicable to human beings and the 
other applicable to plants, we must be under- 
stood as saying, with reference to horses, cattle, 
dogs, and all other domesticated animals, sub- 
stantially the same things which we say with 
reference to human beings. 
The carbonic acid naturally present in the 
atmosphere exists just in sufficient quantity to 
supply food to plants without inflicting any in- 
See the arti- 
VENTILATION. 571 
siderable increase, in a confined apartment, it 
becomes highly noxious to every breathing crea- 
ture. Now during the combustion of wood or 
coal or any other ordinary fuel, or during the 
decomposition of straw or any other dead vege- 
table matter, carbonic acid is formed by the 
combination of the extricated carbon of the fuel 
or litter with the oxygen of the air. This acid 
is formed also by the oxygen consumed in res- 
piration, combining with the carbon in the 
venous blood, which, having become carbonised 
in its progress through the arteries for the pur- 
poses of life, goes to the lungs to be decarbon- 
ised. Thus carbonic acid is given out by the 
breath, as well as by the exhalant pores of the 
body, it being supposed that much uncombined 
oxygen enters the blood, and does not unite with 
carbon until it reaches the capillary arteries. 
This formation of carbonic acid in the body 
engenders animal heat; and oxygen being a 
supporter of the combustion originated by elec- 
trical action—indeed the only supporter of com- 
bustion for living creatures—if the formation of 
carbonic acid actually take place in the capillary 
vessels, we must, according to the views of Dr. 
S. Smith, be burning carbon at every pore of our 
bodies. Though grateful and beneficial to the 
stomach, though constituting one of the princi- 
ples of spirit, wine, and every vinous beverage, and 
though existing as a most wholesome ingredient 
in the water we drink, carbonic acid is a most 
deadly poison to the lungs, and, unless largely 
diluted with atmospheric air, causes instant 
death to him who breathes it. One adult human 
being emits through the lungs and pores of the 
body about 40,000 cubic inches of carbonic acid 
every day,—an amount the carbon of which 
would be equal to nearly three quarters of a 
pound of pure charcoal. Thus four individuals, 
living and breathing in a room eight feet by 
twelve, and eight in height, would, in the twenty- 
four hours, evolve in its space 160,000 cubic feet 
of carbonic acid, or three pounds of solid char- 
coal,—a quantity that would deprive the whole 
of them of life, if all ingress of atmospheric air 
were prevented. Nor is this all. Certain other 
gases are constantly emitted from the bodies 
of living animals, in the form of exhalation 
or insensible perspiration; and are the chemical 
products or recombinations of useless, injurious, 
or morbid and rejected portions of their food 
and organisms; and escape from their pores, or 
are thrust out of their system, in a manner 
strictly analogous to excrementition; and act 
more or less poisonously on every species of ani- 
mals, but most of all on individuals of the same 
species as those by whom they are emitted. The 
chief of these gases are sulphuretted hydrogen, 
phosphuretted hydrogen, and ammonia,—sub- 
stances constituting animal fetor. It is a re- 
markable fact that hydrogen, which, by itself, is 
a quiet odourless gas, an antiseptic, a non-con- 
jury on animals; but whenever it acquires con- | ductor of the electric principle, and a positive 
