260 PHYSICAL SCIENCE BK. vi 



being stagnant through some fault in the earth or 

 the sluggish movement and the everlasting darkness 

 that prevails, is dangerous to breathe. Or being 

 poisoned by the fumes of the internal fires, when it 

 is released from its long inactivity, it taints and 

 pollutes this pure clear air above, and brings new 

 forms of disease to those who inhale the unwonted 

 draught. You remember, too, that we found the 

 water lurking in the secret depths to be useless 

 and even pestilential, since activity never stirs 

 it, and the free breath of heaven never ruffles it. 



3 Being therefore thick and covered beneath gross 

 eternal darkness it contains only elements that are 

 pestilential and injurious to our bodies. So, too, the 

 atmosphere, which mingles with it and lies amid 

 these marshes, scatters far and wide its poison when 

 it issues out, and kills those who breathe it. The 

 flocks, which the pestilence is wont to attack, feel 

 the poisonous effects more readily, because they are 

 more greedy in feeding. They live for the most 

 part in the open, and they drink a great deal of 

 water, which is chiefly responsible for the pestilence. 



4 Sheep are of rather delicate constitution, and, as 

 they keep their heads close to the earth, I am not 

 surprised at their being attacked by the infection ; 

 they receive the blasts of tainted air just as it issues 

 from the ground. If it had issued in greater volume, 

 it would have injured man too. But the abundant 

 supply of pure air counteracted it before it could 

 rise high enough to be breathed by any human 

 being. 



