222 



The veins differ from arteries ia possessing thinner walls, less elastic 

 and muscular tissue, and for the most part a stronger tunica adventitia. 

 They collapse when cut across or when they are empty. The majority 

 of veins are provided with valves ; these are folds of the lining mem- 

 brane, strengthened by fibrous tissue. They favor the course of the 

 blood and prevent its reflux. The nerves which supply both the ar- 

 teries and the veins come from the sympathetic system. The smaller 

 arteries terminate in the system of minute vessels, known as the cap- 

 illaiies, which are interposed between the termination of the arteries 

 and the commencement of the veins. Their average diameter is about 

 one three-thousandth of an inch. 



SOUNDS OF THE HEART. 



By placing the ear behind the elbow against the left side of the chest 

 two distinct sounds can be heard at each heart-beat in health. The first 

 is rather muffled and prolonged, the second is short and sudden. The 

 first is caused by the contraction of the ventricles, the closing of the 

 auriculo-ventricular valves, and the forcible propulsion of the blood into 

 the arteries; the second follows immediately, and is due to the reflux 

 of the blood just forced into the arteries, and the sudden closure of the 

 valves which prevent its return to the heart. In disease of the heart 

 or valves these sounds are generally modified, or supplanted by others, 

 which vary so much in character and are so diflicult to describe that we 

 can not consider them here ; long and extensive experience is required 

 to distinguish them practically. 



CHARACTERS OF THE PULSE. 



The circulation of the blood through the heart is constant, and is 

 maintained by the propelling activity of this organ. In the horse the 

 heart beats from thirty-six to forty-six times a minute, varying with the 

 disposition, breed, and temperament of the animal. In the foal the 

 pulse is about three times as rapid as in the adult, from six months to 

 a year about twice as quick, and in the two-year-old about one-quarter 

 faster. The pulse is usually taken at the angle of the jaw, where the 

 artery crosses the bone, and its force or character is often indicative of 

 the nature of the disease from which an animal may besufl"ering. The 

 pulse, therefore, is named in accordance with its character as slow, soft, 

 small, full, weak, quick, hard, irregular, intermittent, venous, etc. 



Slow pulse is one where the number of beats are less than normal, and 

 is often found in certain diseases of the brain. 



Soft or compressible pulse is one where the beat is rather weak, bat not 

 abnormally rapid. It is often found in debility due to want of assimi- 

 lation or proper nourishment. When accompanied with fever or loss 

 of appetite it is usually indicative of derangement of the digestive 

 organs. 



