16 THE HARVEIAN ORATION, 1894. 



quently to increase the resistance which the left ventricle has 

 to overcome. Moreover, in the case of the intestinal vessels, 

 there is a special provision made for preventing their contrac- 

 tion from causing too great a rise of arterial pressure. This 

 consists in the depressor nerve, which passes from the heart and 

 tends to produce dilatation of the abdominal vessels, and thus 

 to prevent any undue pressure occurring within the heart from 

 their excessive corxtraction. But in the case of the muscles, we 

 have no such nerve. Its place seems to be taken by the dilating 

 fibres which occur in the motor nerves. As I have already said, 

 however, their power to dilate the muscular vessels may be at 

 first more than counteracted by mechanical compression at the 

 commencement of exertion. Thus the blood pressure in the 

 ■arteries, and the resistance which it opposes to the contraction 

 and emptying of the ventricle, may be unduly increased at first 

 by any effort, especially if it be sudden or severe. 



^4s a general rule, the distension of any hollow muscular 

 organ is attended with great pain. How great is the suffering 

 when obstruction of the bowel prevents evacuation of its con- 

 tents ; or when calculi, in their passage down the gall duct or 

 oireters, forcibly distend their walls. One of the severest tor- 

 tures of the middle ages was to distend the stomach with water, 

 and the Emperor Tiberius could imagine no more awful punish- 

 ment for those whom he hated than to make them drink wine, 

 and, at the same time, by means of a ligature, to prevent the 

 ■distended bladder from emptying itself. The heart is no 

 •exception to this rule, and distension of its cavities brings on 

 most acute physical suffering. Its inability to empty itself is a 

 question of relative, and not of absolute power ; for a strong 

 heart may be unable to work only against enormously increased 

 resistance in the peripheral arterioles, while a heart, weakened 

 hj degeneration, may be unable to empty itself in face of 

 pressure little, if at all, above the normal. 



When the contractile power of the heart is not, as it is in 

 health, considerably in excess of the resistance opposed to it in 

 the vessels, but is only nearly equal to it, a slight increase in the 

 resistance may greatly interfere with the power of the heart to 

 empty itself, and bring on pain varying in amount from slight 



