32 FIRESIDE SCIENCE. 



lady will spend hours in a crowded theatre, ball- 

 room, or lecture-room, and take into her lungs a 

 gaseous mixture which has already traversed the 

 air passages and impinged upon the lung cells of 

 perhaps hundreds of men and women. If she 

 should learn that her tooth-brush at any time had 

 come in contact with the surfaces over which this 

 air passed, it would be speedily cast aside, and a 

 new one purchased. 



But it is the chemical change which results in air 

 when respired that renders it unfit for further use. 

 It is reasonable to suppose in fact, we know 

 that rebreathed air is little less than poison to the 

 blood. Consumption and scrofula are found in inti- 

 mate connection with imperfectly ventilated sleep- 

 ing apartments, school-rooms, living-rooms, etc. A 

 vigorous constitution may fight bravely and persist- 

 ently against the influence of the poison ; but the 

 crash comes at last. No one can subsist for many 

 years upon rebreathed air. 



Animals suffer from it as unmistakably as man, 

 and similar diseases are produced in them. The 

 lions and tigers and bears and hyenas confined in 

 menageries, kept close and warm, die speedily of 

 consumption. True tubercle is produced ; weak- 

 ness, emaciation, death, results. It may be that 

 the carbon is retained unoxidized, and that, by fur- 

 ther chemical action, it is forced into new combina- 



