xxvin POISONS UNDERGROUND 261 



XXVIII 



Now you may infer that the earth contains many i 

 deadly elements from the mere fact that so many 

 poisons grow of themselves without being sown ; 

 the soil no doubt contains seeds of evil as well as of 

 good. Is it not the case that, earthquakes apart, 

 in several places in Italy a pestilential steam is 

 emitted through certain openings, which it is not 

 safe for either man or beast to breathe ? Even birds, 

 if they meet it before it is neutralised by the purer 

 breath of heaven, fall in mid -flight ; their bodies 

 become livid, and their jaws swell just as if they had 

 been strangled. As long as this air is contained in 2 

 the earth and escapes by a narrow opening, it has no 

 greater power than to kill creatures that look down 

 into, or voluntarily approach too near, it. But when 

 for centuries darkness has brooded over it, and the 

 gloom of the place has increased the infection, it 

 becomes more dangerous through mere lapse of 

 time ; the more sluggish it is, all the more deadly 

 does it become. Then when it has gained an exit it 

 lets loose all that mischief conceived in the cold 

 shades through endless ages of nether darkness, 

 tainting with it the atmosphere of our realms of 

 earth. The better is ever conquered by the worse. 3 

 Even that purer, air of heaven then changes to 

 pestilential. Thence come sudden and continuous 

 deaths, and portentous forms of disease that spring 

 from unexampled causes. The disaster is long or 

 short lived, according to the strength of the sources 

 of infection. Nor does the plague cease until the 

 freedom of heaven and the tossing of the winds 

 have banished 1 that fatal air. 



1 Or purified. 



