AIR AND VENTILATION 87 



resistance to disease, especially that of an infectious nature, a pro- 

 tracted and often unsatisfactory recovery from illness, and an 

 inability to produce strong and vigorous offspring. 



Not only is the natural resistance to disease lowered, but the 

 air itself in a badly ventilated building may contain large numbers 

 of pathogenic bacteria. The contagium^of influenza, pneumonia, 

 glanders and tuberculosis, to name only a few diseases, has less 

 chance to remain virile and to find receptive hosts in a well ven- 

 tilated, dry and cool building than in one in which the air is 

 constantly foul, warm and moist. Ansemia in the human subject 

 is a well recognised sequence to habitual confinement in badly ven- 

 tilated rooms. Whether dairy cattle confined month after month 

 in equally adverse conditions suffer in a similar manner has not been 

 clearly demonstrated, but it is known that poultry do. Mackenzie 

 and Russel, who have carefully studied the hygienic housing of 

 these birds, especially remark on the anaemic look of birds kept 

 in close houses, and say that they are more liable to tuberculosis 

 and diphtheretic roup, and that egg production is not so prolific 

 during the winter months as when the houses are suitably built and 

 ventilated. They quote Gilbert's Canadian experiments which 

 showed that chickens hatched from eggs laid by birds living in ill- 

 ventilated houses are delicate. 



VENTILATION. 



The problem of ventilation is one that arises owing to the 

 necessity of housing animals in order to protect them from incle- 

 ment weather, to provide for them a convenient resting-place at 

 night, and for economy in attendance. 



In order to rectify the pollution that takes place in an animal 

 house it is necessary to supply to the building an amount of fresh 

 air proportionate with the rate and degree of such pollution. It 

 is therefore necessary to estimate what amount of fresh air is 

 required for each species of animal that is to be kept in confinement. 



It is scarcely possible to supply too much fresh air as no atmos- 

 phere can be too pure, and it is essential for the health of the 

 animals that the supply be not stinted, for if pollution goes on at a 

 greater rate than purifying air is admitted, there must come a time 

 when the air would be so foul as to be distinctly harmful. 



In times past many persons responsible for the construction of 

 animal houses approached the subject with the idea that a stable or 

 byre must shut out fresh air in order that the temperature within 

 might be kept high. 



