THE CIRCULATION OF THE BLOOD AND LYMPH 157 



plexus, sciatic, etc.), which they reach from the sympathetic 

 ganglia by the grey rami communicantes. 



The outflow of vaso-dilator fibres, which also takes place 

 through the anterior roots, does not seem to be restricted to 

 any particular part of the cord, although their existence has 

 been most clearly demonstrated in nerves springing from those 

 regions of the cerebro-spinal axis from which vaso-constrictor 

 fibres do not arise, and where, therefore, we have not to 

 contend with the difficulty of interpreting mixed effects. 

 Some even emerge in the roots of origin of certain of the 

 cranial nerves, as the trigeminus, although many of the 

 vaso-dilator fibres contained in the trunk of this nerve 

 distal to the Gasserian ganglion are derived from the cervical 

 sympathetic, and originally come off from the upper dorsal 

 portion of the spinal cord. The vaso-dilators appear upon 

 the whole to pursue much the same course towards the 

 periphery as the vaso-constrictors, although they often run 

 for a greater distance after leaving the cord without 

 losing their medulla. But eventually they too come into 

 relation with ganglion cells, sometimes scattered along their 

 course, or lying near or in the organs to which they are 

 distributed ; and as in the case of the vaso-constrictors, 

 these ganglion cells with their axis-cylinder processes con- 

 tinue the nervous path to the periphery. It is believed that 

 every vaso-motor fibre is interrupted by one, and only by 

 one, ganglion cell between the cord and the bloodvessels. 



Effect of Nicotine on Nerve-cells. A method which has been 

 found most fruitful in studying the relations of sympathetic ganglion 

 cells to the vaso-motor fibres, as well as to the pilo-motor* and 

 secretory fibres which in certain situations are so intricately mingled 

 with them, must here be mentioned. It depends upon the fact that 

 when a suitable dose of nicotine (10 milligrammes in a cat) is in- 

 jected into a vein, or a solution is painted on a ganglion with a 

 brush, the passage of nerve-impulses through the ganglion is blocked 

 for a time (Langley). The seat of the * block ' is probably the felt- 

 work of fibrils in which the central nerve-fibres terminate around the 

 ganglion cells (Cushny and Huber). The nerve-fibres peripheral to 

 the ganglion are not affected. The question whether efferent fibres 

 are connected with nerve-cells between a given point and their 



* Pilo-motor nerves supply the smooth arrector pili muscles, whose 

 contraction causes the hair to ' stand on end.' 



