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HIGHLAND AND AGRICULTURAL SOCIETY. 
easily detected and avoided than the exciting causes of the malady. 
There are many circumstances which operate as predisposing causes 
to influenza. The most common and most active of these are 
insufficient ventilation, overcrowding, want of cleanliness, and 
defective drainage, to which alone we shall at present advert. 
Insufficient ventilation acts injuriously on all animals, by re- 
ducing their vigour and their disease-resisting powers. Unless 
the air in which animals have breathed for some time be frequently 
renewed, it becomes so altered as to be incapable of affording proper 
support to the vital functions. It contains an excess of carbonic 
acid and a deficiency of oxygen, and such a mixture cannot readily 
enter the lungs or displace the vitiated gases which are brought there 
for excretion, nor can it cause in those worn-out particles of the 
body the effectual oxidation essential to their speedy removal, and 
hence to the health of the animal. Indeed, when a confined portion 
of air contains even so little as 3 per cent, of carbonic acid formed 
at the expense of the oxygen, it speedily proves fatal both to man 
and the lower animals. But the air undergoes still further changes, 
unfitting it for the important purposes it has to serve. It becomes 
surcharged with moisture and unduly heated, and, from its ex- 
pansion, each volume contains a less weight of oxygen. There is 
also present, in a state of incipient decomposition, a great excess of 
these organic matters which are being constantly given off in greater 
or less amount in the breath of all animals. Few things are more 
injurious to animal life than organic matters in a state of decom- 
position. Every one has heard of the serious consequences of 
wounds received while dissecting the human body, of the eating of 
sausages, oysters, or other food in a state of partial decay, and of 
the inhalation of gases evolved from putrifying matters, and these 
are but examples of what invariably occurs when organic matters in 
that state of molecular change which we recognise under the name 
of putrefaction find access to the blood. The amount of organic 
matters in this state given off by the lungs at each expiration is 
very inconsiderable in animals in good health ; but we note its 
existence in the peculiar smell of the breath, and have often still 
further evidence of it in the odours which too often assail the 
nostrils on entering close ill-ventilated stables. These odours, we 
may be told, are only partially owing to this cause, consisting in 
great part of exhalations from the skin and urine, but such ex- 
halations are of a similar kind, and have a similarly injurious effect. 
Further, an animal placed in a confined portion of air renders that 
air irrespirable, not only by pouring into it the effete matters from 
the lungs, but also by evolving similar products from the skin. 
By this channel the body during health and in a pure atmosphere 
gets rid of large quantities both of water and of carbonic acid. 
Lavoisier estimated that 15 grains of insensible perspiration are 
given off every minute from the skin of an averaged-sized man, 
and the quantity in the horse must be much greater. A large 
proportion of carbonic acid is also evolved and oxygen absorbed by 
the skin, and the vital importance of this function of the skin is 
