864 INFLUENCE OF THE NERVOUS SYSTEM. 



Sympathetic systems interpenetrate one another ; each having its own series 

 of ganglionic centres, and of trunks connected with them ; but each system 

 transmitting its fibres into the trunks of the other, so as to be peripherally 

 distributed with their ramifications. Giannuzzi 1 has made a special study 

 of the rami communicautes of the great sympathetic cord in Mammals by 

 the Wallerian method that is, by dividing particular roots of the spinal 

 cord, and after the lapse of a certain period examining the rami comrauni- 

 cantes microscopically with the object of determining whether any, and if 

 any, what amount of degeneration of the nerve-fibres had taken place. 

 The results of his observations are that, with the exception of a few fibres, 

 the fibres of the rami communicautes are entirely derived from the spinal cord, 

 or at least have their nutritive centres in the posterior spinal ganglia, and 

 in the spinal cord. The few exceptional fibres are characterized by their 

 great delicacy and the want of double contours, and pass from the sympa- 

 thetic ganglia through the rami to the roots of the spinal cord. They may 

 be entirely absent. The number of motor fibres sent by the spinal cord to 

 the Sympathetic is greater than the number of sensory fibres. Giannuzzi 

 has also ascertained that the trophic influence of the spinal cord extends 

 along the nerves derived from the spinal cord after they have traversed a 

 sympathetic ganglion. Arndt 2 describes the ganglia of the Sympathetic as 

 composed of an apparently homogeneous matrix, through which granules 

 giving off from 2 to 4 fine processes, are distributed. According to Friiut- 

 zel, 3 the cells of the sympathetic and of the spinal ganglia are invested by 

 a capsule of connective tissue formed by an expansion of the neurilemma of 

 the nerves, which is lined by a layer of pavement epithelium. Beale, Arnold, 

 and others describe a single straight fibre emerging from the nucleus of each 

 sympathetic cell ( 444), and a spiral fibre that appears to be in connection 

 with the surface of the cell, and which, after winding for a few turns round 

 the straight fibre, pursues an opposite direction ; such cells must be regarded 

 as bipolar. There is some doubt whether the cells of the spinal ganglia 

 present this structure or not; Schwalbe 4 and Courvoisier 5 having only been 

 able to discover one fibre originating from each cell ; the cells of these gan- 

 glia are therefore unipolar. 



71 2. The connections and distribution of the principal trunks and branches 

 of the Sympathetic system may be concisely stated as follows : In the cer- 

 vical portion of the sympathetic the presence of the following nerve-fibres 

 appears to have been satisfactorily demonstrated. 6 1. Vaso-motor nerves for 

 the corresponding half of the head, that probably arise from a centre situ- 

 ated in the medulla oblongata, which governs the tone not only of these ves- 

 sels, but of the entire vascular system throughout the body. This ganglionic 

 centre is constantly in action. Its influence can be abolished by section of 

 the spinal cord in the cervical region, and may be reflectorially depressed, 

 as Cyon and Ludwig have shown, by irritation of the depressor nerve, which 

 is a centripetal branch of the vagus ( 242, 244, 245). A local depression 

 of its influence may be also reflectorially induced by irritation of the sensory 

 nerve supplying any part, 7 whilst its action may be excited through the 

 agency of carbonic acid. 2. Fibres distributed to the dilator pupilhe, that 

 probably arise from the oculo-pupillary or cilio-spinal centre, seated in the 



1 Ricorche esequite ncl sjabinctto di Fisiologia ddla It. Univcrsita <li Siena., 1872, 

 p. 51. SIM- nlso Mayer, Wicn. Akad. Sit/,. -her., Bd. Ixvi, Abth. 3, p. 52. 

 * Sclinltxc's Arch'iv f. Mic. Anut., Bd. x, p. 208. 



3 Virrhow's Arcliiv, 1SH7, p MO. 4 Scbultze's Archiv, Bd. iv, p. 45. 



6 Ibid , Bd. ii, p. l:',, and Bd. iv, p 125. 



6 SIT ll<Timinn, (Jrundriss dor Physiologic, 1867, p. 424. 



7 Lovon, Ludwig's Arbeitcn aus dor Physiolog. An.stult zu Leipzig, 1861, p. 1. 



