114 BOARD OF AGRICULTURE. [Pub. Doc. 



and glanders in horses. Hog cholera, swine plague in pigs, 

 distemper in dogs and catarrhal infiammatiou in poultry are 

 familiar examples. 



Malnutrition, enervation, emaciation and inflammation of 

 the mucous membrane of the respiratory tract, are some 

 of the general effects to be observed of the action of impure 

 air. Its tendency is to depress the vital functions and to 

 weaken the natural resistant forces of the body by which 

 disease is j)re vented. 



Properly, the subject of stable ventilation ought to be 

 considered together with other subjects of veterinary 

 hygiene, such as stable construction, including construction 

 of floors, stable drainage, the removal of excrement, stable 

 fixtures, lighting, etc. 



Smith, in his treatise on "Veterinary Hygiene," says: 

 "The objects of ventilation are the supply of pure air to 

 the lungs, the removal from the stable of the products of 

 respiration and cutaneous exhalations and the effluvia arising 

 from the fluid and solid excreta deposited in it." 



Ventilation is produced, says Billings, "By the move- 

 ment of air, and such movement is due to some force, either 

 derived from what may be called the natural conditions of 

 the locality, or specially developed and applied for the pur- 

 pose of producing currents." 



We recognize two great systems of ventilation, namely, 

 artijicial and natural. In artificial ventilation, some other 

 than natural forces are usually employed to move the air. 

 This system is frequently referred to as a forced ventilation, 

 from the fact that the ventilation is efiected by the use of 

 artificially heated chimney flues, by the use of blowers 

 driven by machinery, etc. This system has no practical ap- 

 plication in ordinary stable ventilation, owing to the expense 

 of operation. In the natural system of ventilation we 

 depend upon natural physical forces to rid the stable of im- 

 pure air and to bring in fresh air to take its place. The 

 forces that act are three in number : — 



1. The difierence in weight of masses of air of unequal 

 temperatures. 



2. The law of diff'usion of gases, 

 3.' The force of the wind. 



