AORTIC INSUFFICIENCY IN THE HORSE. I27- 



and then contracts with a degree of energy greater in proportion to the 

 quantity of blood which it contains, and to the diminution in the 

 arterial pressure in the common aorta. Now this more active contrac- 

 tion of the left ventricle is repeated about 50,000 times per twenty-four 

 hours. The increase in work ends by causing hypertrophy of the 

 cardiac muscle, which, for a certain time at least, renders the heart 

 capable of overcoming the increased demand imposed on it b}- the 

 condition of the valves, but which culminates in the period of asystole ;. 

 the heart muscle, enfeebled by over- exertion, undergoes degenerative 

 changes, finally leading to death. The heart may attain very great 

 dimensions. Whilst the medium weight for a healthy heart is about 

 Y^ that of the whole body, a heart with aortic lesions and insufficiency 

 often attains j-^^ to -^^^ of this weight. Sclerotic changes of the 

 muscular substance are rare, because most patients are slaughtered 

 before they can develop. Nevertheless I have seen a certain number 

 of cases in the school, one of which I will describe in a later 

 lecture. 



Aortic insufftciency is indicated by two principal s}'mptoms : (i) a 

 diastolic murmur, loudest at the base of the heart ; (2) a strong pulse, 

 readily perceptible in all accessible arteries. 



The murmur commences with diastole, and continues during the 

 second sound, and a portion, or the whole, of the pause ; it immediatel}' 

 follows the short pause, at the moment when the semilunar valves have 

 returned to their horizontal position, and continues until the first period 

 of the following cardiac cycle, /. e. until the precordial impulse produced 

 by ventricular systole. I said that it was loudest at the base of the 

 heart ; it may also be heard, though less distinctly, as low as the 

 apex, and more rarely in the region above the heart over the aortic 

 trunk. The tone (timbre) of this murmur varies ; usually it is soft 

 and hissing ; sometimes it is rough, grating, or musical. I may add 

 that no close connection can be established between these variations in 

 sound and the age, degree, or peculiarities of the valvular lesions. 



The changes in the pulse are due to the energy with which the 

 ventricle contracts, and to the low blood-pressure in the arterial system. 

 The large wave of blood rapidly injected into relaxed vessels lifts their 

 walls suddenly, and to a greater degree than normal ; but, as consider- 

 able quantities immediately leak back towards the ventricle through 

 the pervious valves, the vessels again collapse, a fact which gives the 

 pulse its peculiar fugitive, elusive character. The pulse is readily 

 discovered by the finger in all accessible arteries, but only in excep- 

 tional cases can it be seen. Few cases of " dancing of the arteries "~ 



