RESPIRATION. 161 



or through the crevices in the upper part of the ceiling, or 

 through a passage-way provided for the purpose. The in- 

 ward current more commonly comes through the uninten- 

 tional crevices which the skill of the architect and mechanic 

 seldom entirely prevents, and which admit air sufficient to 

 save the occupants from the death of the Black Hole, but 

 not enough to save them from some sickness, or faintness, 

 or certainly some depression of life. As those crevices are 

 inadequate to supply the air that is needed to sustain the ful- 

 ness of life, every room that is inhabited, and especially every 

 hall that is filled with people, and every school-room, should 

 be provided with means of ventilation sufficient to adinit and 

 to carry away at least seven feet of air a minute for each oc- 

 cupant. For this purpose, a school-room, with forty persons, 

 should have a ventilator a foot square, through vbich the air 

 should move upward at the rate of two hundred ond eighty 

 feet a minute, and as much fresh air should be received.* In 

 ordinary circumstances, air cannot be compressed ; no more 

 can be received into a room than is carried out. It is there- 

 fore useless to provide means for the admission of fresh air 

 by a furnace or otherwise, unless there be some avenue, 

 either accidental or designed, for the foul air to escape. 

 Nor can a room be emptied of air ; none will go out unless 

 as much comes in. A ventilator will not, then, carry away 

 the foul air, unless there be .some place accidentally left, or 

 especially provided, for the admission of other air to take 

 its place. t 



* This current of air upward is accelerated by placing a large burning lamp 

 in the flue of the ventilator. In most school-houses, a larger ventilator 

 one measuring four or more square feet will be better, and will carry off 

 the foul air sufficiently with a slower current 



t " Experiments have been made, in a room prepared expressly for the pur- 

 pose 5 and in the House of Commons, every day of the session, for two years; 

 and the results show that it was rare to meet with a person who was not 

 sensible of the deterioration of the air when supplied with less than ten cubic 

 feet per minute." Wyman on Ventilation. 



For the best practicable methods of ventilation of dwelling-houses, school- 

 rooms, and public halls, Dr. Wyman's valuable work can be advantageously 

 consulted. 



14* 



