1883.] THE VENTILATION OF FARM BUILDINGS. 201 



nocuous; it can be increased somewhat without injury, but it is 

 decidedly prejudicial to breathe for a long time air containing one 

 measure in 100 of carbonic acid; it is considered desirable that the 

 measure should never exceed one in 500. We may assume that 

 twenty cubic feet of air pass through the lungs every hour, to re- 

 duce the poison to one per cent, at which point it is barely respira- 

 ble; it requires to mingle with as much fresh air as will make a 

 mixture of 100 cubic feet, and, to make the dilution entirely safe, 

 it must be carried five times as far. To state it simply, the respira- 

 tion of one individual requires 500 cubic feet of fresh air per hour. 

 I have placed this estimate quite low; some authorities place it as 

 high as 1,600 cubic feet per hour, but I select the lower, believing 

 it to be nearer the truth, and not desiring to astonish you with 

 large figures, and perhaps receive from you the name of being a 

 sensational speaker. I make no estimate of the contaminating 

 influence of other sources of vitiated air, as the exhalations from 

 the skin, the excretions, etc. 



In making an estimate for horses and cattle, it is customary to 

 allow three times as much air for each individual as in the case of 

 man, but, if we multiply by five, we shall gain far better results. 

 A pig, if he is kept in a clean place, will require about the same 

 quantity as a man; as he is usually kept, however, I am surprised 

 that the race did not become extinct long years ago; it speaks well 

 for his vitality. Works on architecture will provide you with any 

 number of rules for finding the amount of fresh air required in the 

 various buildings of the farm, such as multiplying various dimen- 

 sions together, and dividing, by certain imaginary figures, but in 

 actual use they are of no account, and I leave them without con- 

 sideration. 



Before touching upon the mechanical principles of ventilation, it 

 is perhaps necessary to call attention to the fact that the virulence 

 of poisoned air does not so much depend upon any known con- 

 dition of the gases as upon the personal condition of the victim, 

 such as age, state of health, etc. A vitiated air may be breathed 

 with impunity in hours of activity, that would produce serious 

 ailments if breathed when the system is in the non-resistant con- 

 dition of sleep, or even rest. As an illustration of this fact we 

 may mention that serious troubles have time and again been traced 

 to the sewers of Paris, but that zymotic diseases are comparatively 

 rare among the 600 men who find employment within them. 



