100 PHYSIOLOGY AND HEALTH. 



mental labor, for it is difficult for them to fix their attention 

 upon their studies; and they are fatigued with the ineffectual 

 attempts to learn that which at other times is easy. But the 

 moment they are dismissed, they run eagerly from the im- 

 pure air of the room to the pure atmosphere abroad, and 

 then feel a return of life, and even a glow of exhilaration. 



385. Whenever, in these and other ways, the lungs are not 

 supplied with a sufficiency of pure air or oxygen, life is de- 

 preciated, and this depreciation is in proportion to the foul- 

 ness of the air. If men dwell in rooms that are perfectly air- 

 tight, so that no fresh air can be admitted, all the oxygen is 

 soon consumed, and then their blood can be relieved of no 

 more of its burden of dead atoms, and the vital powers, 

 not being sustained, sink, and life is as effectually extin- 

 guished as it would be if they were buried in the water. In 

 this manner, one hundred and twenty-three men died in the 

 Black Hole of Calcutta.* The difference between the faint- 

 ness and languor of a crowded room and the death in the 

 Black Hole is a difference only in degree, but not in kind; 

 and it is only by step after .step, in the same course of cor- 

 rupting atmosphere and depreciating life, that our children 

 in the unventilated school-rooms, and our sleepers in the 

 small chambers, and our audiences in crowded lecture-rooms, 

 might go from the inconvenience they there feel to the 

 death from which they shall awake no more. 



386. If breathing air loaded with more than three and a 

 half per cent, of carbonic acid gas be injurious, the breath- 

 ing this gas in its pure state is destructive. This gas is 

 heavier than the air, ( 295, p. 134,) and therefore it falls to 

 the bottom of a vessel or room, like water. Hence it is un- 

 safe for a living creature to go to the bottom of wells and vats 

 that contain it. Fire will not burn in this gas. Workmen, 



* One hundred and forty-six persons were shut up in a room, called tiie 

 Black Hole of Calcutta, on the night of the 20th of June, 1756. This room 

 was eighteen feet square, and eighteen feet high, " open only by two windows, 

 strongly barred, from which they could scarcely receive the least circulation 

 of air." " \t the dawn of day, only twenty-three persons remained alive out 

 of one hundred and forty-six." 



