354 AMERICAN FARMER'S HORSE BOOK. 



afforded by the air-cells. In these the blood is purified, by the pro- 

 cesses of decarbonizaiion and oxygenizaiion. They unite and form the 

 pulmonary veins, one of which is indicated in the cut, near the up- 

 permost of the downward-pointing arrows, but is not lettered. 



Gj The left auricle of the heart, which receives the now purified, or arterial- 

 ixed, blood from the pulmonary veins, and from which it passes to the 

 left ventricle. 



JJ, The left ventricle, the contraction of whose powerful walls forces the blood 

 out through the aorta and the successive subdivisions of the arteries 

 to all parts of the system. 



/, The aorta posterior, dividinj^ and subdividing into smaller arteries, which 

 finally unite with the capillaries at A, where begins once more the 

 venous circulation. The aorta posterior is the great artery which 

 supplies the abdomen and all the hrnd extremities with blood. The 

 latter is now freighted with nutrition extracted in the intestines 

 from the food, and conveyed into the general circulation through the 

 thoracic duct (not shown in the cut) and the anterior vena cava. 



J^ The trunk of the aorta anterior, the great artery which supplies the con- 

 tents of the thorax, or chest, and all the fore extremities, etc., with 

 the pure and nutriticJ^ blood. It ramifies and terminates in the 

 same manner as the aorta posterior. 



DISEASES OF THE HEART. 



The causes and symptoms of this entire class of diseases 

 are very obscure. Perhaps hypertrophy, or enlargement of 

 the heart, is the most common affection- A Mr. Thomson, 

 of Bath, England, several years ago, contributed to veterinary 

 science the history of a singular case, in which the heart be- 

 came *'a large disorganized mass, weighing thirty-four 

 pounds." Other cases have been reported much nearer 

 home ; but hardly any thiug seems to be known respecting 

 the disease, beyond its simple existence. Of course the pro- 

 cess of growth must be going on for some time before it kills 

 the horse ; yet there are no certain means by which the exist- 

 ence of such a condition can be detected. If the action of 

 the heart be seriously obstructed, the animal must die at 

 once, and a comparatively slight 'derangement would occasion 

 acute suffering. In rnany, or perhaps nearly all, cases of 

 death from this disease, the heart seems to have performed 

 its usual functions, without noticeable disturbance, up to the 

 very moment of its entirely ceasing to beat. 



In regard to any other disease of the heart, we must con- 



