678 SYMPATHETIC AND OTHER SYSTEMS OF NERVES. 



ments have gone, dyspnoea increases and chloroform decreases the 

 paralytic secretion. 1 But the sympathetic ganglia supplying the hairs 

 do not appear to acquire any tonic action after severance from the 

 spinal cord. 



Lastly, it remains to mention the belief once held, that the beat of 

 the heart is caused by rhythmic impulses from the local ganglia. This 

 view is now generally abandoned. The discussion of it belongs else- 

 where. We may, however, notice the possibility that the local ganglia 

 have even after section of the vagus, a tonic inhibitory action upon the 

 heart. 



ON PERIPHEKAL GANGLIA AS CENTRES FOR DEFINITE AREAS. 



It is conceivable that the peripheral nerve cells should be collected 

 together according to their function, so that all the vaso-constrictor 

 nerve cells which send their axons to a given area should be collected 

 into one ganglion, the vaso-dilator nerve cells in another ganglion, the 

 pilo-motor in a third, and so on. But in fact, within the limits of each 

 division of the autonomic system, there is no instance in which this 

 occurs. It occurs only when a tissue receives fibres from two divisions 

 of the autonomic system ; then the ganglia of the two systems are 

 separated, and they may have different functions. What we find is 

 that a ganglion which sends nerve fibres to a particular area sends to it 

 all the varieties of nerve fibres, received by the area from the autonomic 

 system to which the ganglion belongs. When an area receives axons 

 from the sympathetic and from the cranial system, or from the 

 sympathetic and from the sacral system, the axons from the two 

 systems have each their own ganglion, and some variety of nerve cell 

 may be, and indeed commonly is, present in the ganglion of the one, 

 which is not present in the ganglion of the other. 



Each ganglion, then, may be regarded as a group of nerve cells 

 supplying fibres of various functions to a definite area. In some cases, 

 and within the limits of each autonomic system, all nerve cells supply- 

 ing a given area are collected together to make one ganglion, but this 

 simple arrangement is commonly departed from in one, or in both, of 

 two ways. For there is a tendency for the nerve cells supplying an 

 area to be arranged in several small ganglia instead of in one larger 

 one. Thus, instead of a single ciliary ganglion, there may be one main 

 ganglion and several accessory ganglia. So the ganglia for the various 

 abdominal and pelvic viscera usually consist of a main ganglion and of 

 accessory ganglia. And even the vertebral ganglia may be in two 

 parts, a small part occurring in the course of a grey ramus. 



Further, as we have seen, there is some overlapping in the areas 

 supplied by the several ganglia. The overlapping may be constant and 

 considerable, as in the case of the ganglia sending axons to the hind- 

 limbs; it may be constant and slight, as in the case of some of the 

 thoracic ganglia sending fibres to the skin of the back ; or it may be 

 variable, both in occurrence and extent, as in the case of ganglia which 

 may send fibres by a white ramus as well as by a grey one. 



EEFLEX ACTIONS FROM AUTONOMIC GANGLIA. 



Experimental observations on reflex actions from autonomic ganglia 

 were first made by Bernard with regard to the ganglion called by him 



1 Langley, Journ. PhysioL, Cambridge and London, 1885, vol. vi. p. 71. 



