Prof. Huxley on the Structure and Functions of Nerve. 73 



ceases. The pneuinogastiic nerves must act either directly u|)on 

 the muscles of the heart, or indirectly through the ganglia, into 

 which they can he traced. If the former alternative be adojjted, 

 then we must conceive the action of the pneumogastric nerve upon 

 muscle to be the reverse of that of all other nerves — for irritation 

 of every other muscular nerve causes activity and not paralysis of 

 the muscle. Not only is this in the highest degree improbable, but 

 it can be demonstrated to be initrue ; for on irritating, mechanically, 

 the surface of the heart brought to a standstill by irritation of the 

 pncumogastrics, it at once contracts. The paralysing influence, 

 therefore, is not exerted on the muscles, and as a consequence, we 

 can only suppose that this "negative innervation," as it might be 

 conveniently termed, is the result of the action of the pneumogastric 

 on the ganglia. 



It results from all these experiments, first, that nerve-substance 

 possesses the power of exciting and coordinating muscular actions ; 

 and secondly, that one portion of nervous matter is capable of con- 

 trolling the action of another portion. In the case of the heart it 

 is perfectly clear that consciousness and volition are entirely excluded 

 from any influence upon the action of the nervous matter, which 

 must be regarded as a substance exhibiting certain phsenomena, 

 whose laws are as much a branch of physical inquiry as those pre- 

 sented by a magnet. 



Now, (still carefully excluding the phsenomena of consciousness,) 

 we shall find on careful examination, that all the properties of 

 Nerve are of the same order as those exhibited by the nervous 

 substance of the heart. Every action is a muscular action, whose 

 proximate cause is the activity of a nerve, and as the muscles of the 

 heart are related to its ganglia, so are the muscles of the whole 

 body related to that great ganglionic mass which constitutes the 

 spinal marrow, and its continuation the medulla oblongata. This 

 cranio-spinal nervous centre originates and coordinates the con- 

 tractions of all the muscles of the body independently of conscious- 

 ness, and there is every reason to believe that the organ of con- 

 sciousness stands related to it as the pneumogastric is related to the 

 cardiac ganglia ; that volition, whether it originates, or whether it 

 controls action, exerts its influence not directly on the muscles, but 

 indirectly upon the cranio-spinal ganglia. A volition is a conscious 

 conception, a desire ; an act is the result of the automatic, uncon- 

 scious origination and coordination, by the cranio-spinal ganglia, 

 of the nervous influences required to produce certain muscular 

 contractions. 



Whatever may be the ultimate cause of our actions then, the 

 proximate cause lies in nerve-substance. The nervous system is a 

 great piece of mechanism placed between the external world and 

 our consciousness ; through it objects affect us ; through it we afi'ect 

 them ; and it therefore becomes a matter of the highest interest 

 to ascertain how far the properties and laws of action of nerve- 

 substance have been ascertained by the physiological philosopher. 



Nerve-substance has long been known to consist of two ele- 



