6^8 



NA TURE 



[October 25, 1894 



whenever the roan began to think, the increased supply of 

 blood to his brain caused the head to go down and the heels to 

 rise up. A similar condition was indicated by Mayow, who 

 gave a different explanation. He said that the vital spirits were 

 not able to be in the same place at once, and therefore it hap- 

 pens that if a man eats a heavy meal, he is apt to become drowsy, 

 because the vital spirits descend from the brain to the stomach 

 in order to carry on digestion ; and, on the other hand, if a 

 man thinks vigorously after dinner, the vital spirits have to 

 leave the stomach to go tj the brain, and consequently digestion 

 is imperfectly performed. If we substitute the word blood for 

 vital spirits, we have an exact expression of present physio- 

 logical ideas. 



Ubi stimulus ihi afflu.vus was an old doctrine and expressed 

 a great truth. Wherever the need for increased nourishment or 

 increased supply of oxygen exists in the healthy body, thither 

 does the blood llow in larger quantities than usual. If the glands 

 are active, their blood supply is greatly increased, as was shown 

 by Bernard, and a similar occurrence takes place in the contract- 

 ing muscle, as has been shown by L'tdwig and his scholars. 

 The vessels of the intestines and of the skin, with their numerous 

 glands, have their calibre regulated by the vaso motor nerves 

 which proceed from the centre in the medulla oblmgata. This 

 centre acts most readily upon the vessels of the intestine, and 

 rather less readily on those of the skin. In consequence of this, 

 when the centre is irritated, the vessels of the intestine contract 

 and drive the blood through the skin, so that it is warmer than 

 before, and it is only when the stimulation is very great that the 

 vessels of both contract .'io that the skin receives less blood than 

 normal, and becomes colder than before. But if the vessels of 

 the skin and intestine are both contracted, where does the blood 

 go? This question was put by Ludwig, and answered by the 

 experiments which he made with Hafiz. It is evident that if the 

 heart be stopped while the blood pressure is being measured in the 

 artery of an animal, the pressure will fall regularly and steadily, 

 because the blood is flowing out all the time through the ar- 

 terioles and capillaries into the veins. One would naturally 

 expect that if the arterioles were contracted by irritation of the 

 vaso motor centres in the medulla, the fall of blood pressure 

 would either not take place at all, or would be very much slower 

 than before ; but on trying the expcrimenl, Ludwig and Hiliz 

 found, to their surprise, that the blood pressure fell almost as 

 quickly as when the vaso motor cenire was left alone, and the 

 vessels of the skin and intestine therefore remained uncontracted. 

 In other words, the vessels which supply the muscles of the 

 body and limbs are capable of such extension that when fully 

 dilated they will allow the arterial blood to pour through them 

 alone nearly as quickly as it usually does through the vessels of 

 the skin, intestine, and muscles together. This observation, it 

 seems to me, is one of the greatest importance, and one that 

 has hardly received as yet the attention which it merits. 



It is obvious that contraction of the cutaneous vessels, such as 

 occurs upon exposure to cold, will drive more blood through 

 the muscles, and as oxidation goes on more rapidly in them 

 the result will be increased production of heat. 



The experiments I have just mentioned show that the vessels of 

 the muscles are not controlled by the vaso motor centre in th; 

 medulla otilongala in the same way as those of the intestine and 

 skin. How far their vascular centres miy be associated with 

 those for voluntary movements, which have been so a<lmirably 

 lo:allsedby Ferrierin the cerebral cortex, still r.:uiains to be made 

 out. The circulation through the muscles is indeed a complex 

 phenomenon, and it was shown by Ludwig and .Sadler to 

 depend upm at least two factors having an antagonistic action. 

 When a muscle is thrown into action, it mechanically com- 

 pre>se< the blood Vissels within it, and thus tends to lessen the 

 circulation through it, but at the same time the stimulus which 

 is sent down through the motor nerve, and which calls it into 

 action, brings about a dilatation of the vascular walls, and thus 

 increases the circula'ion through the muscle. 



Whei the amount of blood is measured before, during, and 

 after stimulation of its motor nerves, it is sometimes found that 

 the fl'jw is diminished, at others that it is increaiied, the altera- 

 tion depending upon the comparative effect of the mechanical 

 compression of the vessels ol the muscles just mentioned, and 

 upon ih; increase of their lumen by the dilatition of their walls. 

 It invariably happens, however, that after the muscle has ceased 

 to act, the (low of blood through the muscle is increased. This 

 increase is quite independent of any alteration in the general 

 pressure of blood in the arteries, and it occurs when an arti- 



NO. 1304, VOL. .so] 



ficial stream of blood, under constant pressure, is sent through i 

 the muscle. The dilatation in the muscular vessels, .is indicated 1 

 by the increased flow of blood, and consequent chinge of colour 

 in the frog's tongue, was observed by Lepine after stimulation of 

 the peripheral ends of the hypoglossal and glossopharyngeal 

 nerves, and the actual changes in the vessels themselves were 

 observed microscopically by von Frey and Gaskell. 



The dilatation of muscular vessels on irritation of peripheral 

 nerves was thus brought into a line with the dilatation noticed 

 in the vessels of the submaxillary gland by Bernard, and in the 

 corpora cavernosa by Eckhart. It is evident that alteration in 

 the size of such a huge vascular tract as the muscular arteries 

 must influence, to a great extent, the blood pressure in the 

 arteries generally, and it is equally evident that the changes 

 induced in the condition of the blood pressure by muscular 

 action may be of two kinds, either a rise or a fall. If the 

 arterioles are compressed by the muscles so that the flow through 

 them is impeded, the general blood pressure will rise. Whei> 

 this effect is more than counteracted by the dilatation of the 

 arterioles themselves under nervous influence the gener.il blood 

 pressure will fall, for the blood will find an cisy passage 

 through the vessels from the arteries into the veins. We can 

 thus see how readily a rise or fall in the general blood pressure 

 may be induced by exercise of the muscles. If they contract 

 suddenly or violently they will tend to compress the arterioles, 

 and raise the blood pressure, while quite easy contraction wilt 

 have little effect in compressing the arterioles, and these, becom- 

 ing dilated, will allow the blood pressure to fall. 



But there is still another factor which may tend to increase the 

 blood pressure during severe muscular exertion, viz. a quickened 

 pulse for stimulation of the nerve fibres extending from the 

 muscles to the central nervous system greatly accelerates the 

 beats of the heart. In this respect stimulation of the muscular 

 nerves differs from that of the cutaneous and visceral nerves, 

 inasmuch as the latter tend rather to slow than to quicken the 

 pulse. The peculiar eflect of the muscular nerves upon tli 

 heart would, indeed, appear to be a provision of nature for ih. 

 purpose of maintaining an exceedingly active circulation during 

 the active calls upon nutrition which violent exertions entail. 

 Muscular exercise, therefore, h-is a special tendency to raise 

 the blood pressure in the arterial system, and consequently 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 contraction from causing 

 too great a rise of arterial pressure. This consists in the de- 

 pressor nerve, which passes from the heart and tends to produce 

 dilatation of the abdominal vessels, and thus prevent any undue 

 pressure occurring within the heart from their excessive con- 

 traction. 



In the case of the muscles, we have no such nerves. Its 

 place seems to be taken by the dilating fibres which occur ii> 

 the motor nerves. As I have already said, however, this effect 

 of dilatation in the muscular vessels may be at first more than 

 counteracted by mechanical com )ression at the commencement 

 of exertion, and 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. 



As a general rule, the distension of any hollow muscular 

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

 when obstruction of the bowel prevents evacuation of its con- 

 tents ; or when a calculus, in its p.assige down the gall duct or 

 ureter, forcil)ly distends their wall. One of the severest tortures 

 of the Middle Ages was to distend the stomach with water, and 

 the Kmperor Tiberius could imagine no more awful punishment 

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

 at the same lime, by means of a ligature, to prevent the dis- 

 tended bladder from emptying itself. The heart is no excep- 

 tion to this rule, and distcn-ion of its cavities brings on most 

 acute physical suffering. Its inabilily to empty itself is a ques- 

 tion of relative, and not of absolute, power ; for a strong heart 

 may be unable to work only against enormously increased resist- 

 ance in the peripheral arterioles, while the heart, weakened bf 

 degeneration, maybe 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 ia 

 health, considerably in excess of the resistance opposed to it 

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

 sistance may greatly interfere with the power of the heart to 

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

 uneasiness to the most intense ajony in angina pectoris 



