4; 6 MODERN DEVELOPMENTS OF HARVEY's WORK. 



But altli()uj;li these facts were known to ITarvey so long ago, it is 

 only in comparatively recent years that the niechauisin by wliich they 

 are brought about has beeu investigated, and it is only within the last 

 decade that i^hysiologists have begun regularly to believe that the 

 cardiac muscle has ii power of rhythmic pulsation independent of its 

 nerves, although Harvey had noted that when the heart was cut into 

 small pieces the fragments would still continue to pulsate. We may 

 fairly, indeed, compare the movements of the heart, as regarded by 

 physiologists of the present day, to those of a horse, which is capable 

 of going independently, although its i)ace may be slowed (u- accelerated 

 by the reins or spur of the rider. The power of the vagus to act as a 

 rein to the heart, and slow its movements or stop them altogether, was 

 first noted by Edward and Ernest lleinrich Weber, while the effect 

 that it sometimes has of accelerating instead of slowing, like the effect 

 of shaking the reins of the horse, was observed by Schitt', Moleschott, 

 and Lister. 



The accelerating nerves of the heart, and the position of the nerve 

 center from which they spring, were more thoroughly investigated by 

 von Bezold,^ Avhile the power of the vagus to weaken as mcII as slow the 

 heart Avas observed by Gaskell. The position of the cardiac center, 

 which, like the rider, regulates the movements of the heart, was located 

 in the medulla oblongata chiefly by Ludwig and his scholars. Like the 

 heart, the vessels also are regulated in diameter by the nervous system 

 in accordance with the wants of the body generally; and the eflect 

 upon the vasomotor uerv^es, which when cut allow them to dilate and 

 when stimulated cause them to contract, was discovered by Bernard, 

 Brown-Sequard, and by our countryman, Waller; Avhile the power of 

 other nerves to cause immediate dilatation was discovered by Bernard, 

 Eckhardt, and Ludwig in the submaxillary glands, penis, and periph- 

 eral vessels, respectively. 



The heart when cut out of the body still continues to beat, and the 

 transmission of excitation from one cavity to another was experimented 

 on by Paget, although removed completely from the influence of the cen- 

 tral nervous system, and the vessels have a somewhat similar power of 

 independent contractility. The alterations produced in the circulation 

 generally and locally by the contractile power of the vessels and the 

 changes caused in the vessels by the central nervous system by periiih- 

 eral stimulation of the nerves or by variations in the quality of the 

 blood have formed the subject of a series of researches extending over 

 many years, and though originated and in many cases entirely conducted 

 by Ludwig have appeared to a great extent under the names of his pupils. 

 The starting point of these investigations was an examination of the 

 changes in the blood as it flowed through isolated organs, with the view 

 of ascertaining in what manner the combustion by which the animal heat 



'Voii Bezold. UntcrsiR'buugeii iiber die luucrvatiou des Herzeiis, 18G3. l^eipzig: 

 EiiKehiiuuu. 



