16 DISEASES OF THE HOBSB. 



ture or occurs late in an infectious disease. In nearly all of the dis- 

 eases of the heart and in anemia the pulse becomes rapid. 



The pulse is irregular in diseases of the heart, and especially where 

 the valves are affected. The irregularity may consist in varying inter- 

 vals between the beats or the dropping of one or more beats at regu- 

 lar or irregular intervals. The latter condition sometimes occurs in 

 chronic diseases of the brain. The pulse is said to be weak, or soft, 

 when the beats are indistinct, because little blood is forced through 

 the artery by each contraction of the heart. This condition occurs 

 when there is a constriction of the vessels leading from the heart and 

 it occurs in certain infectious and febrile diseases, and is an indication 

 of heart weakness. 



In examining the heart itself it is necessary to recall that it lies in 

 the anterior portion of the chest slightly to the left of the median line 

 and that it extends from the third to the sixth rib. It extends almost 

 to the breastbone, and a little more than half of the distance between 

 the breastbone and the backbone. In contracting, it rotates slightly 

 on its axis, so that the point of the heart, which lies below, is pressed 

 against the left chest wall at a place immediately above the point of 

 the elbow. The heart has in it four chambers — ^two in the left and 

 two in the right side. The upper chamber of the left side (left auri- 

 cle) receives the blood as it comes from the lungs, passes it to the 

 lower chamber of the left side (left ventricle) , and from here it is sent 

 with great force (for this chamber has very strong, thick walls) 

 through the aorta and its branches (the arteries) to all parts of the 

 body. The blood returns through the veins to the upper chamber of 

 the right side (right auricle), passes then to the lower chamber of the 

 right side (right ventricle), and from this chamber is forced into the 

 lungs to be oxidized. The openings between the chambers of each 

 side and into the aorta are guarded by valves. 



If the horse is not too fat, one may feel the impact of the apex of 

 the heart against the chest wall with each contraction of the heart by 

 placing the hand on the left side back of the fifth rib and above the 

 point of the elbow. The thinner and the better bred the horse is the 

 more distinctly this impact is felt. If the animal is excited, or if he 

 has just been exercised, the impact is stronger than when the horse is 

 at rest. If the horse is weak, the impact is reduced in force. 



The examination of the heart with the ear is an important matter in 

 this connection. Certain sounds are produced by each contraction of 

 the normal heart. It is customary to divide these into two, and to 

 call them the first and second sounds. These two sounds are heard 

 during each pulsation, and any deviation of the normal indicates some 

 alteration in the structure or the functions of the heart. In making 

 this examination, one may apply the left ear over the heavy muscles 

 of the shoulder back of the shoulder joint, and just above the point of 



