MODERN DEVELOPMENTS OF HARVEY's WORK. 471 



causing no violent exertion of tlie muscles, produces no mechanical con- 

 striction of the vessels, and thus does not increase the blood pressure. 

 The greater exertion of walking up a hill has this effect, but if the 

 patient is able to continue his exertions, the increased dilatatiou of the 

 vessels — a consequence of muscular activity — allows the i)ressurc again 

 to fall and relieves the pain. 



As muscular exertion continues and the vessels of the muscles 

 become dilated, the flow of blood from the arteries into the veins will 

 tend to become much more rapid than usual. The pressure iu the 

 arterial system will consequently fall, but that in the veins will become 

 increased, and unless a corresponding dilatation occurs in the pulmo- 

 nary circulation, blood will tend to accumulate in the right side of the 

 heart, the right ventricle will be unable to empty itself completely, 

 shortness of breath will arise, and even death may occur. At first the 

 right side of the heart is affected, and the apex beat disappears from 

 the normal place and is felt in the epigastrium, but the left ventricle 

 also becomes dilated, though whether this is simply through nervous 

 influence tending to make it act concordantly with the right, or for 

 some other reason, it is at present impossible to say. Severe exertion, 

 even for a few minutes, may produce this condition in healthy persons,^ 

 and when the exertion is overcontinued it may lead to permanent mis- 

 chief. More especially is this the case in young growing boys, and 

 it is not merely foolish, it is wicked to insist upon boys engaging in 

 games or contests which demand a long-continued overexertion of the 

 heart, such as enforced races and paper chases extending over several 

 miles. Intermittent exertion, either of a single muscle or of a groui^ of 

 muscles, or of the whole body, appears to lead to better nutrition and 

 increased strength and hypertrophy, but overexertion, especially if it 

 continues, leads to impaired nutrition, weakness, and atrophy. If we 

 watch the movements of young animals, we find that they are often 

 rapid, but fitful and irregular and varied in character, instead of being 

 steady, regular, and uniform. They are the movements of the butterfly, 

 and not of the bee. The varied plays of childhood, the gambols of the 

 lamb, and the frisking of the colt are all well adapted to increase the 

 strength of the body without doing it any injury; but if the colt, 

 instead of being allowed to frisk at its own free will, is put in harness, 

 or ridden iu races, the energy which ought to have gone to growth is 

 used up by the work, its nutrition is affected, its iwwers diminished, 

 and its life shortened. The rules which have been arrived at by the 

 breeders of horses ought to be carefully considered by the teachers of 

 schools, and by the medical advisers who superintend the pupils. 



In youth and middle age every organ of the body is adapted for doing 

 more work than it is usually called ui)on to do. Every organ can, as 

 it is usually termed, make a spurt if required; but as old age comes on 

 this capacity disappears, the tissues become less elastic, the arteries 



' Schott. Verbandl. ties IX Congresses in Med. zu Wieu, 1890. 



