ENLARGEMENT OR DILATATION OF THE HEART. I 39 



muscular walls that the disease fully declares itself; presumably 

 because the heart has a capacity for taking in more blood at one 

 time than the walls have the power to drive on through the arter- 

 ial system; consequently the impulse of the heart becomes weaker 

 and the weight of the vital fluid is too much for it to overcome; 

 hence the circulation becomes slow and torpid, and the blood 

 regurgitates, a phenomenon that is readily discernable by that 

 peculiar backward movement in the jugular veins that may fre- 

 quently be seen along the groove in the horse's neck formed 

 mainly by the windpipe; when this pulsation in the veins is 

 observed, attention should at once be directed to the heart, be- 

 cause it is essentially an abnormal condition, the pulse never 

 occurring among veins in health. 



Among the causes to which dilatation of the heart are attribut- 

 able, are frequent overexertion, such as occurs among horses sub- 

 jected to severe training for long-distance races, and hunters or 

 steeple-chasers; it must not be understood from this that we 

 consider horses incapable of being prepared for this sort of work, 

 but the consequences are attributable to the fact that the prepara- 

 tion goes on and is persisted in when the animals are not fit to 

 undergo work demanding so serious a strain upon the vital organ; 

 were this fact recognized at the proper time and suitable measures 

 adopted to remedy the temporary weakness, the animal's consti- 

 tution would recover its natural vigor, and the requisite course of 

 training and preparation could be conducted without any subse- 

 quent ill-effects, nay more, the very work itself would tend to 

 render the horse more hardy and capable of taking his own part 

 in the field or between the flags in a satisfactory manner. 



A further cause of dilatation arises from some obstruction to 

 the free and natural circulation of the blood which may be due to 

 defect in the valves of the heart or the large arteries, also to dis- 

 eases of the lungs and kidneys which give rise to some impediment 

 in the circulation by reason of an alteration in the tissues of these 

 organs. When the dilatation of the heart increases while the 

 walls become thinner, the power to drive on the blood is reduced 

 and consequently the pulse is weak, slower than normal and the 

 beat is prolonged; the beats become irregular and intermittent 

 (the meaning of the latter word has already been explained) ; the 

 . breathing becomes difficult ; the legs do not maintain their natural 



