228 BUKEAU OF ANIMAL INDUSTRY. 



vessel. In this coat the nutrient vessels, the vasa va-sorum, form a cap- 

 illary network, from which a few penetrate as far as the muscular coat. 

 The veins differ from arteries in 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 membrane, strengthened by fibrous tissue. They favor the 

 course of the blood and prevent its reflux. The nerves which suppl}' 

 both the arteries and the veins come from the sympathetic sj^stem. 

 The smaller arteries terminate in the system of minute vessels, known 

 as the capillaries, 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. 



DISEASES OF THE HEART AND BLOOD VESSELS. 



In considering diseases of the heart we meet with many difficulties, 

 depending much upon the position which this organ occupies in the 

 animal. The shoulders cover so much of the anterior portion of the 

 chest, and often in very heavy-muscled horses the chest walls are so 

 thick, that a satisfactory examination of the heart is attended with 

 difficulty. Diseases of the heart are not uncommon among horses; 

 the heart and its membranes are frequently involved in cfiseases of 

 the respiratory organs, diseases of the kidneys, rheumatism, influenza, 

 etc. Some of the diseases of this organ are never suspected by the 

 ordinary observer during life, and are so diflacult to diagnose with 

 any degree of certainty that we will have to confine ourselves to a 

 general outline, giving attention to such symptoms as maj^ serve to 

 lead to a knowledge of their existence, with directions for treatment, 

 care, etc. 



Nervous affections often produce prominent heart symptoms l)y 

 causing functional disturbance of that organ, which, if removed, will 

 leave the heart restored to perfect vigor and normal action. Organic 

 changes involving the heart or valves, however, usually grow worse 

 and eventually prove fatal. Therefore it is necessary that we arrive 

 at an appreciation of the true nature and causes, so that we may be 

 able to form a true estimate of the possibilities for recovery or en- 

 couragement for medical treatment. 



Disease of the heart may occur at any age, but it is witnessed most 

 frequently in j^oung horses, which, when being trained for fast work, 

 are often subjected to excessive hardship and fatigue. Nervous or 

 timid animals also suffer from such diseases more frequentl}" than 

 those of a sluggish disposition. Any cause which induces a violent 

 or sudden change in the circulation ma}^ result in injur}' to the heart. 

 Symptoms which may frequently denote disease of the heart are diffi- 

 cult breatiiing or short-windedness, dropsies of the limbs, habitual 



