120 BL'REAU OF ANIMAL INDUSTRY. 



(little lobes). A little ])ronchial tube terminates in every one of these 

 lobules. The little tube then divides into minute branches which 

 open into the air cells (pulmonary vesicles) of the lunjrs. The air cells 

 are little sacs having a diameter varying from one-seventieth to one 

 two-hundredth of an inch; the}^ have but one opening, the communi- 

 cation with the branches of the little bronchial tu])es. Small blood 

 vessels ramify in the walls of the air cells. The air cells arc the 

 consummation of the intricate structures forming the respiratory 

 apparatus. They are of prime importance, all the rest being com- 

 plementary. It is here that the exchange of gases takes place. As 

 before stated, the walls of the cells are very thin; so, also, are the 

 walls of the blood vessels. Through these walls escapes from the 

 blood the carbonic acid gas that has been absorbed by the blood in its 

 circulation through the different parts of the body; and through these 

 walls is absorbed by the blood, from the air in the air cells, the oxygen 

 gas which is the life-giving element of the atmosplicre. 



CONGESTION OF THE LUXGS. 



Congestion is essentially an excess of blood in the vessels of the 

 parts affected. Congestion of the lungs in the horse, when it exists 

 as an independent affection, is generally caused by overexertion when 

 the animal is not in a fit condition to undergo more than moderate 

 exercise. Veiy often what is recognized as congestion of the lungs 

 is but a symptom of exhaustion or dilatation of the heart. 



The methods practiced by the trainers of running and trotting 

 horses will give an idea of what is termed "putting a horse in condi- 

 tion " to stand severe exertion. The animal at first gets walking 

 exercises, then after some time he is made to go faster and farther 

 each day; the amount of work is daily increased until the horse is 

 said to be "in condition." An animal so prepared runs no risk of 

 being affected Avith congestion of the lungs, if he is otherwise healthy. 

 On the other hand, if the horse is kept in the stable for the purpose 

 of laying on fat or for want of something to do, the muscular sj'stcm 

 becomes soft, and the horse is not in condition to stand the severe 

 exertion of going fast or far, no matter how health}^ he ma}^ be in 

 other respects. If such a horse be given a hai-d ride or drive, he maj' 

 start oft' in high spirits, but soon becomes exhausted, and if he is 

 pushed he will slacken his pace, show a desire to stop, and may stag- 

 ger or even fall. Examination will show the nostrils dilated, the 

 flanks heaving, the countenance haggard, and the appearance of suffo- 

 cation. The heart and muscles were not accustomed to the sudden 

 and severe strain put upon them; the heart became unable to perform 

 its work; the blood accumulated in the vessels of the lungs, which 

 eventually became engorged with the stagnated l)lood, constituting 

 congestion of the lungs. 



