772 THE POPULAR SCIENCE MONTHLY. 



of fifty years much, more vulnerable than the young man ; and 

 vulnerable in precisely the organ most essential to life. It is, in 

 fact, the heart that suffers in case of forced exertion, the conse- 

 quences of a deficient elasticity of the arteries. Every beating of 

 the heart represents the piston-stroke of a force-pump, and the 

 blood-vessels are the pipes through, which the liquid flows to 

 carry life to the furthest molecules of our body. But these ves- 

 sels are not inert conductors ; they are endowed, in a healthy con- 

 dition, with an elasticity which permits them to react at each 

 pulse of the heart, swelling under the pressure of the sanguine- 

 ous wave, and then contracting and returning to the liquid 

 the impulse which they have received from it. The liquid, strik- 

 ing upon the wall of a fully elastic artery, does not suffer at 

 once the arrest which it would suffer on meeting a rigid wall. 

 A billiard-ball, driven against a very elastic cushion, rebounds 

 with nearly as much force as it had when it started. An 

 artery which has lost its elasticity is, as to the column of blood 

 that comes against it, as an ivory ball to a cushion that does 

 not spring. And as the billiard-player must strike more vigor- 

 ously upon the ball to make it perform its run when the cush- 

 ions do not spring, so the heart, when the artery has lost its elas- 

 ticity, must exaggerate its effort at the systole to enable every 

 molecule of blood to traverse the circle of the vessels and return 

 to its point of departure. In short, the less elastic the arteries, 

 the greater the effort the heart has to make to secure equal work. 

 Each heart-beat, then, of a man whose arteries have become old, 

 is the occasion for an excess of labor by the cardiac muscle. The 

 increase in expenditure of force passes unnoticed if the beatings 

 retain their normal slowness, but becomes very sensible when 

 they are quickened. There are some exercises which cause the 

 number of heart-beats to double in a few moments. The resultant 

 fatigue of the organ, which has already been brought to the point 

 of overwork by the continual excess of work it has had to do, is 

 easy to conceive. 



The most natural consequence of fatigue of the heart is a 

 momentary diminution of its energy ; and when the organ is 

 weakened, the impulse it gives to the blood is no longer sufficient 

 to cause it to traverse as rapidly as it ought the vessels through 

 which it circulates with most difficulty, either on account of their 

 narrowness, or of the mass which is precipitated into them at 

 once. Hence what are called passive congestions of the internal 

 organs, and particularly of the lungs. Congestion of the lungs 

 is a frequent consequence in elderly men of exercises which accel- 

 erate to excess the rhythm of the pulse, and is shown by shortness 

 of breath. This, which is more prompt in men habituated to 

 physical exercises, is one of the first symptoms of arterial dete- 



