302 THE CIRCULATION IK THE BLOOD-VESSELS. [CH. XXI. 



animal, stimulation of the anterior nerve-roots produces no move- 

 ments of the involuntary muscles, because the paralysed cell 

 stations on the course of the nerve-fibres act as blocks to the 

 propagation of the impulse. If the nicotine is applied locally 

 by painting it over one or more ganglia, there will be a block in 

 those fibres only which have their cell stations in those particular 

 ganglia. Thus, in the lateral chain of ganglia we find the cells 

 on the course of the pilo-motor nerves (i.e., to the muscles of the 

 hairs), of the vaso-constrictors of the head, limbs, and body walls, 

 and possibly of the splenic nerves. In the collateral ganglia are 

 found, amongst others, the cells on the course of the splanchnic 

 nerves, of the nerves to sweat glands, of the cardiac accelerators, 

 and of the inhibitory fibres of the alimentary canal ; while in 

 the terminal ganglia are placed, among others, the cells on the 

 cardiac inhibitory nerves, on the motor fibres to the lower part 

 of the intestine and bladder, and on the inhibitory fibres to the 

 external genital organs. 



The cell stations on the vaso-constrictors are situated for the trunk in the 

 corresponding lateral ganglia : for the head, neck and salivary glands in 

 the superior cervical ganglion ; for the upper limb in the ganglion stellatum : 

 for the lower limb in the sixth and seventh lumbar, and first and second 

 sacral ganglia ; for the tail in the coccygeal ganglia ; for the stomach in the 

 coeliac ganglion ; for the small intestine in the superior mesenteric ; for the 

 large intestine and rectum in the inferior mesenteric ; and for the external 

 genitals in the sacral ganglia. The cells on the vaso-dilatators are placed in 

 the superior cervical ganglion for the gums and lips ; in the hilus of the 

 gland for the submaxillary ; and near the viscus for the rectum, external 

 genitals, &c. The cells for the motor-fibres of the upper part of the alimentary 

 canal are in the ganglion trunci vagi ; for the lower part on the course of the 

 fibres near the viscus. The cells on the inhibitory fibres of the upper part 

 of the alimentary canal are in the coeliac or superior mesenteric ganglia, and 

 for the lower part in the inferior mesenteric ganglia, or along the course 

 of the hypogastric nerves. 



We may now ask what is the object that is served by the existence of 

 ganglia on the course of these nerves. It appears to be a means of distri- 

 buting nerve-fibres to a vast area of muscular tissue by means of a com- 

 paratively small number of nerve-fibres that leave the central nervous 

 system ; for each fibre that leaves the central nervous system arborises 

 around a number of cells, and thus the impulse it carries is transferred to a 

 number of new axis-cylinder processes. 



In some cases, it is true, a single nerve-fibre will divide into multitudinous 

 branches to accomplish the same object (as in the supply of the electric 

 organ of Malapterurus, the fibres to the millions of its subdivisions all 

 originating from a single axis-oylinder), but the usual way appears to be a 

 combination of this method with that of subsidiary cell-stations. 



At one time a ganglion was supposed to be the seat of reflex action. The 

 submaxillary ganglion was the battle-field in which this question was 

 fought out. In all the researches of Langley and Anderson, who have 

 investigated every ganglion in the body, they have never found that a 

 ganglion is the seat of a reflex action. The only instances where such a 

 thing seemed possible were the following: When all the nervous connections 

 of the inferior mesenteric ganglion are divided except the hypogastric 

 nerves, stimulation of the central end of one hypogastric causes contraction 



