112 



VETERINARY STUDIES 



trol of temperature and moisture. Mere motion, aside from its 

 relation to other factors, has not been shown to be important 

 for stock. 



Natural forces. — The factors that operate in natural ventila- 

 tion are : the force of the wind ; the weight of air, as varied by 

 its temperature ; the diffusion of gases in obedience to a natural 

 law; and the force of the wind is probably the most important 

 one of these factors, and must always be taken into considera- 

 tion in planning ventilation or in making mathematical esti- 

 mates of the amount of air needed. The force of the wind is, 

 of course, irregular ; but variations can be made in the ventilat- 



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Fig. 38. — Ventilation. (Paige.) 

 Air Currents. Manger front inlet. 



ing facilities to compensate for this. The incoming air should 

 not pass over, or through, any contaminating source, such as 

 a manure pile, and it is very important that the general plan of 

 construction should be well considered. 



Temperature and weight.— The second factor, difference in 

 weight between the lighter warm and heavier cold air, is not 

 so important in natural (windows and doors) as in artificial 

 ventilation, and yet it is a factor of considerable importance. 

 The heat which warms the air in the lower levels is that 

 which comes from the bodies of the confined animals, as it is 

 radiated from the surface or warmed in passing through the 



lungs. 



Diffxision of ^as^es.— Carbonic gas is considerably heavier than 

 air, but the lower air levels usually do not usually show much 

 more CO2 than the higher ones on account of diffusion, which 

 takes place in response to the law of diffusion of gases — operat- 

 ing independently of relative weights. This force is so strong 



