CONDITIONS AFFECTING THE VASO-MOTOR CENTRE. 6jJ 



in the medulla oblongata, the blood-vessels are acted upon by local or subordinate 

 vaso-motor centres in the grey matter of the spinal cord, as is proved by the follow- 

 ing observations : If the spinal cord of an animal be divided, then all the blood- 

 vessels supplied by vaso-motor nerves below the point of section are paralysed, as 

 the vaso-motor fibres proceed from the medulla oblongata. If the animal lives, 

 the blood-vessels regain their tone and their former calibre, while the rhythmical 

 movements of their muscular walls are ascribed to the subordinate centres in the 

 lower part of the spinal cord (Lister, Goltz 362, 7). 



The subordinate spinal centres may, further, be stimulated directly by dyspnceic blood, and 

 also reflexly, in the rabbit and frog ( Ustimowitsch). After destruction of the medulla oblongata, 

 the arteries of the frog's web still contract reflexly when the sensory nerves of the hind leg are 

 stimulated (Putnam, Nussbaum, Vulpian). In the dog, opposite the 3rd to 6th dorsal nerve is a 

 spinal vaso-motor centre (origin of the splanchnic), which can be excited reflexly (Smirnow), 

 and there is a similar one in the lower part of the spinal cord ( Vulpian). 



If the lower divided part of the cord be crushed, the blood-vessels again dilate, 

 owing to the destruction of the subordinate centres. In animals which survive this 

 operation, the vessels of the paralysed parts gradually recover their normal diameter 

 and rhythmical movements. This effect is ascribed to ganglia, which are supposed 

 to exist along the course of the vessels. [It is to be recollected that the existence 

 of these peripheral nervous mechanisms has not been proved.] These ganglia [or 

 peripheral nervous mechanisms] might be compared to the ganglia of the heart, and 

 seem by themselves capable of sustaining the movements of the vascular wall. 

 Even the blood-vessels of an excised kidney exhibit periodic variations of their 

 calibre (C. Ludwig and Mosso). It is important to observe that the walls of the 

 blood-vessels contract as soon as the blood becomes highly venous. Hence, the 

 blood-vessels offer a greater resistance to the passage of venous than of arterial 

 blood (C. Ludivig). Nevertheless, the blood-vessels, although they recover part of 

 their tone and mobility, never do so completely. 



The effects of direct mechanical, chemical, and electrical stimuli on blood-vessels may be due 

 to their action on these peripheral nervous mechanisms. The arteries may contract so much 

 as almost to disappear, but sometimes dilatation follows the primary stimulus. 



Lewaschew T found that limbs, in which the vaso-motor fibres had undergone degeneration, 

 reacted like intact limbs to variations of temperature ; heat relaxed the vessels, and cold con- 

 stricted them. It is, however, doubtful if the variations of the vascular lumen depend upon 

 the stimulation of the peripheral nervous mechanisms. Amyl nitrite and digitalis are supposed 

 to act on those hypothetical mechanisms. 



The pulsating veins in the bat's wing still continue to beat after section of all their nerves, 

 which is in favour of the existence of local nervous mechanisms {Luchsinger, Schiff). 



, ; Influence of the Cerebrum. The cerebrum influences the vaso-motor 

 Centre, as is proved by the sudden pallor that accompanies some psychical con- 

 ditions, such as fright or terror. There is a centre in the grey matter of the 

 cerebrum where stimulation causes cooling of the opposite side of the body. 



Although there is one general vaso-motor centre in the medulla oblongata, which 

 influences cdl the blood-vessels of the body, it is really a complex composite centre, 

 consisting of a number of closely aggregated centres, each of which presides over a 

 particular vascular area. We know something, e.g., of the hepatic ( 175) and renal 

 ceutres ( 276). 



Many poisons excite the vaso-motor nerves, such as ergotin, tannic acid, copaiba, and cubebs ; 

 others first excite, and then paralyse, e.g., chloral hydrate, morphia, laudanosin, veratrin, 

 nicotin, Calabar bean, alcohol: others rapidly paralyse them, e.g., amyl nitrite, CO ( 17), 

 atropin, muscarin. The paralytic action of the poison is proved by the fact that, after section 

 of the vagi and accelerantes, neither the pressor nor the depressor nerves, when stimulated, 

 produce any effect. Many pathological infective agents affect the vaso-motor nerves. 



The veins are also influenced by vaso-motor nerves, and so are the lymphatics, 

 but we know very little about this condition. 



Pathological. The angio-neuroses, or nervous affections of blood-vessels, form a most 

 important group of diseases. The parts primarily affected may be either the peripheral nervous 



