CHAPTER IV. 
ATMOSPHERE OF THE CAVE. 
As the circulation of the air, its temperature, 
purity, etc., in the Gave, are subjects upon which 
we are frequently interrogated, and which pos- 
sess great interest to all anticipating a visit, we 
proceed to give the explanation of these points 
in the words of Dr. Wright, who thus treats 
of what he very properly terms the respiration 
of the cave. 
The Mammoth Cave breathes once a year. 
That is to say, in summer, or when the tempera- 
ture of the external air is above that of the 
Cave, the current sets from the latter to the 
former. In other words, the Cave is the entire 
summer in making an expiration. On the other 
hand, when the order is reversed, or the tem- 
perature of the outer atmosphere is below fifty- 
nine degrees, the Cave makes an inspiration, 
or draws in its breath, which it accomplishes 
during the winter. The respiratory mechanism 
of the Cave ceases to operate—or, to carry out 
: (43) 
