DISEASES OF THE EESPIRATORY OBGANS. ''Ill 



plied to the breast is a beneficial adjunct. The diet should be the 

 most nourishing. Bulky feed should not be given. Linseed mashes, 

 scalded oats, and, if in season, grass and green-blade fodder are the 

 best diet. 



THE LUNGS. 



The lungs (see PI. VII) are the essential organs of respiration. 

 They consist of two (right and left) spongy masses, commonly called 

 the " lights," situated entirely withia the thoracic cavity. On account 

 of the space taken up by the heart, the left lung is the smaller. Ex- 

 ternally, they are completely covered by the pleura. The structure of 

 the lung consists of a light, soft, but very strong and remarkably 

 elastic tissue, which can be torn only with difficulty. Each king is 

 divided into a certain number of lobes, which are subdivided into 

 numberless lobules (little lobes). A little bronchial 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 

 lungs. The air cells are little sacs having a diameter varying from 

 one-seventieth to one two-hundredth of an inch; they have but one 

 opening, the communication with the branches of the little bronchial 

 tubes. Small blood vessels ramify in the walls of the air cells. The 

 air cells are the consummation of the intricate structures forming 

 the respiratory apparatus. They are of prime importance, all the 

 rest being complementary. 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; through 

 these walls also the oxygen gas, which is the life-giving element of 

 the atmosphere, is absorbed by the blood from the air in the air cells. 



CONGESTION OF THE LUNGS. 



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. Very 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 he is said to 

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



