DISEASES OF THE RESPIRATORY APPARATUS 93 



The lobule is the smallest divisiuu of the luug and is formed 

 by capillary bronchial tubes, air cells and blood-vessels. It is 

 here that the external respiration or the exchange of gases be- 

 tween the capillaries and the air cells occurs. 



Ventilation. — It is agreed by all persons who have investi- 

 gated the subject, that unventilated stable air is injurious to 

 animals. At one time it was believed that the injurious effects 

 resulting from the breathing of air charged with gases and 

 moisture from the expired air and the animal's surroundings, 

 were due to a deticiency in oxygen. It is now l)elieved that the 

 ill-effects are mainly due to the stagnation of air, the humid 

 atmosphere, and the irritating gasee emanating from the body 

 excretions. 



The common impurities for^d in stable air are carbonic and 

 ammonia gas, moisture charged with injurious matter and dust 

 from the floor and bodies of the animals. As a rule, the more 

 crowded and filthy the stable, the more impurities there are in 

 the air. If any of the animals are affected with an infectious 

 disease, such as tuberculosis or glanders, the moisture and dust 

 may act as carriers of the disease-producing germs. Infectious 

 diseases spread rapidly in crowded, poorly ventilated stables. 

 The two factors responsible for this rapid spread of disease are 

 the lowered vitality of the animal, due to breathing the vitiated 

 air, and the greater opportunity for infection, because of the 

 comparatively large number of bacteria present in the air. 



The purpose of stable ventilation is to replace the stable 

 air with purer air. The frequency with which the air in the 

 stable should be changed depends on the cubic feet of air space 

 provided for each animal, and the sanitary conditions present. 

 The principal factor in stable ventilation is the force of the 

 wind. In cold weather it is very difficult to properly ventilate 

 a crowded stable without too much loss of animal heat and 

 creating draughts. 



For practical purposes, the need of ventilation in a stable 



