COURSE OF THE VASO-MOTOR FIBRES. 673 



influences the vaso-motor centre, we may thus explain the influence of psychical excitement 

 (speaking, &c.) upon the cessation of haemorrhage. If the haemorrhage be severe, stimulation 

 of the medulla oblongata, due to the anaemia, may ultimately cause constriction of the small 

 arteries, and thus arrest the bleeding. Thus, surgeons are acquainted with the fact that 

 dangerous haemorrhage is often arrested as soon as unconsciousness, due to cerebral anaemia, 

 occurs. If the heart be ligatured in a frog, all the blood is ultimately forced into the veins, 

 and this result is also due to the anaemic stimulation of the oblongata {Goltz). In mammals, 

 when the heart is ligatured, the equilibration of the blood-pressure between the arterial and 

 venous systems takes place more slowly when the medulla oblongata is destroyed than when it 

 is intact (v. Bezold, Gscheidlen). 



[Effect of Destruction of the Vaso-motor Centre. If two frogs be pithed and their hearts ex- 

 posed, and both be suspended, then the hearts of both will be found to beat rhythmically and 

 fill with blood. Destroy the medulla oblongata and spinal cord of one of them, then immedi- 

 ately in this case, the heart, although continuing to beat with an altered rhythm, ceases to be 

 filled with blood ; it appears collapsed, pale, and bloodless. There is a great accumulation of 

 the blood in the abdominal organs and veins, and it is not returned to the heart, so that the 

 arteries are empty. This experiment of Goltz is held to show the existence of venous tonus 

 depending on a cerebro-spinal centre. If a limb of this frog be amputated, there is little or no 

 haemorrhage, while in the other frog the haemorrhage is severe. The bearing of this experi- 

 ment on conditions of "shock" is evident.] 



Action of Poisons. Strychnin stimulates the centre directly, even in curarised dogs, and so 

 do nicotin and Calabar bean. 



Direct Electrical Stimulation. On stimulating the centre directly in animals, it is found that 

 single induction shocks only become effective when they succeed each other at the rate of 2 to 

 3 shocks per second. Thus there is a "summation" of the single shocks. The maximum 

 contraction of the arteries, as expressed by the maximum blood-pressure, is reached when 10 to 12 

 strong, or 20 to 25 moderately strong shocks per second are applied (Kronecker and Nicolaides). 



Course of the Vaso-motor Nerves. From the vaso-motor centre fibres proceed directly through 

 some of the cranial nerves to their area of distribution ; through the trigeminus partly to the 

 interior of the eye ( 347, I., 2), through the lingual and hypoglossal to the tongue ( 347, III., 

 4), through the vagus to a limited extent to the lungs ( 352, 8, 2), and to the intestines 

 ( 352, 11). 



All the other vaso-motor nerves descend in the lateral columns of the spinal cord ( 364, 9) ; 

 hence, stimulation of the lower cut end of the spinal cord causes contraction of the blood-vessels 

 supplied by the nerves below the point of section (Pffiiger). In their course through the cord, 

 these fibres form connections with the subordinate vaso-motor centres in the grey matter of the 

 cord ( 362, 7), and then leave the cord either directly through the anterior roots of the spinal 

 nerves to their areas of distribution, or pass through the rami communicantes into the sympa- 

 thetic, and from them reach the blood-vessels to which they are distributed ( 356) [see fig. 439]. 



The following is the arrangement of these nerves in the region of the head : The cervical 

 'portion of the sympathetic supplies the great majority of the blood-vessels of the head (see 

 Sympathetic, 356, A, 3). In some animals, the great auricular nerve supplies a few vaso- 

 motor fibres to its own area of distribution (Schiff, Loven, Moreau). The vaso-motor nerves to 

 the upper extremities pass through the anterior roots of the middle dorsal nerves into the 

 thoracic sympathetic, and upwards to the 1st thoracic ganglion, and from thence through the 

 rami communicantes to the brachial plexus {Schiff, Cyon). The skin of the trunk receives its 

 vaso-motor nerves through the dorsal and lumbar nerves. The vaso-motor nerves to the lower 

 extremities pass through the nerves of the lumbar and sacral plexuses into the sympathetic, 

 and from thence to the lower limbs (PflUger, Schiff, CI. Bernard). The lungs, in addition to a 

 few fibres through the vagus, are supplied from the cervical spinal cord through the 1st thoracic 

 ganglion [Brown- Sdquard, FicJc and Badoud, Lichtheim). The splanchnic is the greatest vaso- 

 motor nerve in the body, and supplies the abdominal viscera ( 356, B v. Bezold, Ludwig and 

 Cyon). The vaso-motor nerves of the liver ( 173, 6), kidney ( 276), and spleen ( 103) have 

 been referred to already. According to Strieker, most of the vaso-motor nerves leave the spinal 

 cord between the 5th cervical and the 1st dorsal vertebrae. [Gaskell finds that in the dog (fig. 

 439) they begin to leave the cord at the 2nd dorsal nerve ( 366).] 



As a general rule, the blood-vessels for the skin of the trunk and extremities are innervated 

 from those nerves which give other fibres (e.g., sensory) to those regions. The different vascular 

 areas behave differently with regard to the intensity of the action of the vaso-motor nerves. 

 The most powerful vaso-motor nerves are those that act upon the blood-vessels of peripheral 

 parts, e.g., the toes, the fingers, and ears; while those that act upon central parts seem to be 

 less active (Lewaschew), e.g., on the pulmonic circulation ( 88). 



II. Reflex Stimulation of the Centre. There are fibres contained in the 

 different afferent nerves, whose stimulation affects the vaso-motor centre. There 

 are nerve-fibres whose stimulation excites the vaso-motor centre, thus causing a 



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