116 



To give a rude idea of the arrangement of the respiratory apparatus 

 as a whole, we may profitably compare it to a tree, for the want of a 

 better illustration. Say that all the respiratory tract from the nasal 

 openings back to the pharynx are the roots in the ground; the larynx 

 may be compared to the large part of the trunk just above the earth; 

 the windpipe will represent the body or the bole of the tree; the right 

 and left bronchi may be considered the first two or largest limbs ; the 

 bronchial tubes are then comparable to all the rest of the limbs, 

 branches and twigs, gradually becoming smaller and. branching out 

 more frequently, until the smallest twigs terminate by having a leaf 

 appended; and to complete the comparison we may as well say the 

 leaf will do to represent the air-cells. Now, imagine all parts in and 

 around the limbs, branches, twigs, and leaves filled in with some mate- 

 rial (say cotton or tow) and the whole covered over with silk or satin 

 to about the beginning of the branches on each of the first two large 

 limbs. The cotton or tow represents the lung-tissue and the silk or 

 satin covering will represent the pleura. It must be admitted that 

 this is rather a rough Avay to handle such delicate structures, but if 

 the reader is possessed of a good imagination he may gain, at least, a 

 comprehension of the subject that will suffice for the purpose of being 

 better able to locate the various diseases and appreciate the mechan- 

 ism of the resiairatory organs in their relations to each other. 



CONGESTION OF THE LUNGS. 



Inflammation of the lungs is always preceded by congestion, or, to 

 make it plainer, congestion may be considered as the first stage of 

 inflammation. Congestion is essentially an excess of blood in the 

 A'essels of the parts affected. Congestion of the lungs in the horse, 

 v.iien it exists as an independent affection, is generall}^ caused by 

 overexertion when the animal is not in a fit condition to undergo more 

 than moderate exercise. 



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 prei)ared 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 i)urpose 

 of laying on fat or for want of something to do, the muscular system 

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

 exertion of going fast or far, no matter hoAv healthy he may be in 

 other respects. If such a horse be given a hard ride or drive, he may 

 start off 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 



