164 ANATOMY OF THE SPINAL MARROW, OF GANGLIA, 



Ganglia feel like hard knots, of a minute size upon nerves ; 

 but their substance is in fact as soft and pulpy as that of 

 the brain itself. The feeUng of hardness is owing to a very 

 dense covering of neurilema, which acts to each as a tiny 

 cranium. The ganglia are the centres of reflex motion : 

 that is, a sentient nerve is tickled, say of the bottom of the 

 foot, and the feeling is carried to a ganglion ; thence it is 

 transmitted to the nerves that set us laughing. The feeling 

 may be painful, but nevertheless we cannot help ourselves 

 but laugh. This is called reflex action, when a motor or 

 sentient nerve is excited ; and in consequence of this a dif- 

 ferent nerve, or opposite set of nerves, are called into action. 

 The gangha likewise presides over the sympathetic nerve ; a 

 nerve which is independent of the brain ; and by the con- 

 tinued health of which we may live long and yet exist quite 

 unconsciously. 



The sympathetic nerve. — This nerve presides over secre- 

 tion ; and is the centre of those functions which are necessary 

 to life ; as the brain is the centre of all acts under the con- 

 trol of volition. Thus, a man may will he shall not feel 

 hungry, and the will may in some degree master the sensa- 

 tion ; but at length the sympathetic nerve exerts its power, 

 the abstinence becomes painful, and the sense of pain is 

 conveyed to the brain by the eighth pair of nerves. The 

 sympathetic is most obvious in the abdomen, where it forms 

 numerous plexuses ; of which the solar is the largest. From 

 these plexuses it twists round the arteries ; and by these is 

 conveyed all over the body, or wherever the blood travels ; 

 and where does it not ? Wherever the vital fluid exists the 

 sympathetic is known also to be. Beside this, the numerous 

 ganglia from which it derives independence of action, 

 answer the end of little brains, and are distributed through- 

 out the body. They are discerned even within the brain 

 itself; and fresh discoveries render us uncertain where they 

 do not exist. The sympathetic is essentially the nerve of 

 organic life; that is, it presides over secretion, excretion, 

 nutrition ; and all those functions which, independent of the 

 brain, are imperative for the preservation of existence. It 

 is well seen along the neck, where it travels within the 

 sheath of the carotid artery ; better within the chest and 

 abdomen, as a well defined line below the ribs, upon the 



