712 EEPORT— 1881. 



which, taken together, must be regarded as of equal importance with the original 

 discovery of Harvey. First, it was found by Henle that the arterial blood-vessels 

 by which blood is distributed to brain, nerve, muscle, gland, and other or^-ans, are 

 provided with muscular walls like those of the heart itself, by the contraction or 

 dilatation of which the supply is increased or diminished according to the require- 

 ments of the particular organ. Secondly, it was discovered simultaneously, but 

 independently, by Brown-Sequard and Augustus Waller, that these arteries are 

 connected by nervous channels of influence with the brain and spinal cord, just as 

 the heart is. Thirdly, it was demonstrated by Bernard, that what may be called 

 the heart-managing channels spring from a small spot of grey substance in the 

 medulla oblongata, which we now call the ' heart-centre ' ; and a little later by 

 Schiff', that the artery-regulating channels spring from a similar head-central office, 

 also situated in the medulla oblongata, but higher up, and from subordinate cen- 

 tres in the spinal cord. 



If I had the whole day at my disposal and your patience were inexhaustible, 

 I might attempt to give an outline of the issues to which these five discoveries' 

 have led. As it is, I must limit myself to a brief discussion of their relations to 

 each other, in order that we may learn something from them as to the nature of 

 automatic action. 



Sir Isaac Newton, who although he knew nothing about the structure of nei'ves, 

 made some shrewd forecasts about their action, attributed to those which are con- 

 nected with muscles an alternative function. He thought that by means of motor 

 nerves the brain could determine either relaxation or contraction of muscles. Now 

 as regards ordinary muscles we know that this is not the case. We can will only 

 the shortening of a muscle, not its lengthening. When Brown-S^quard dis- 

 covered the function of the motor nerves of the blood-vessels, he assumed that the 

 same limitation was applicable to it as to that of muscular nerves in general. It 

 was soon found, however, that this assumption was not true in all cases — that there 

 were certain instances in which, when the vascular nerves were interfered with, 

 dilatation of the blood-vessels, consequent on relaxation of their muscles, took place ; 

 and that, in fact, the nervous mechanism by which the circulation is regulated is a 

 highly-complicated one, of which the best that we can say is that it is perfectly 

 adapted to its purpose. For while every organ is supplied with muscular arteries, 

 and every artery with vascular nerves, the influence which these transmit is here 

 relaxing, there constricting, according (1) to the function which the organ is called 

 upon to discharge : and (2) the degree of its activity at the time. At the same time 

 the whole mechanism is controlled by one and the same central office, the locality 

 of which we can determine with exactitude by experiment on the living animal, 

 notwithstanding that its structure affords no indication whatever of its fitness for 

 the function it is destined to fulfil. To judge of the complicated nature of this 

 function we need only consider that in no single organ of the body is the supply of 

 blood required always the same. The brain is during one hour hard at work, 

 during the next hour asleep ; the muscles are at one moment in severe exercise, the 

 next in complete repose ; the liver, which before a meal is inactive, during the 

 process of digestion is turgid with blood, and busily engaged in the chemical work 

 which belongs to it. For all these vicissitudes the tract of grey substance which 

 we call the vascular centre has to provide. Like a skilful steward of the animal 

 household, it has, so to speak, to exercise perfect and unfailing foresight, in order 

 that the nutritive material which serves as the oil of life, for the maintenance of 

 each vital process, may not be wanting. The fact that this wonderful function is 

 localised in a particular bit of grey substance is what is meant by the expression 

 ' automatic action of a centre.' 



But up to this point we have looked at the subject from one side only. 



No state ever existed of which the administration was exclusively executive — 

 no government which was, if I may be excused the expression, absolutely absolute. 

 If in the animal organism we impose on a centre the responsibility of govern- 

 ing a particular mechanism or process, independently of direction from above, we 

 must give that centre the means of being itself influenced by what is going on in 

 all parts of its area of government. In other words, it is as essential that there 



