FUNCTIONS OF THE NERVE CELL 313 



practically every nerve of the body. Thus the presence of a crumb on the 

 larynx will excite impulses travelling up the superior laryngeal nerve, which 

 in themselves can involve but little expenditure of energy. The result 

 however of their arrival at the central nervous system is the discharge of 

 impulses along the motor nerves causing spasmodic contractions of almost 

 every muscle in the body. It seems beyond doubt then that energy is 

 evolved in the central nervous system as a result of metabolic changes, and 

 that energy may be added to impulses passing through the central nervous 





FIG. 152. Diagrammatic representation of the brain of Carcinus to show the parts 

 involved in Bethe's experiment. The dotted line x shows the incision employed 

 to isolate the neuropilem of the ganglion of the second tentacle. 



system, which therefore acts as a relay of force. But this activity does not 

 necessarily require the presence or co-operation of nucleated cells. In 

 dealing with the nature of a nerve impulse we had reason to conclude that 

 there may be an actual, though minimal, liberation of energy in the axis 

 cylinder with the passage of each nerve impulse. The non-nucleated parts 

 of a cell, whether the axon or the cell body, are equally capable of this 

 evolution of energy, and we might conceive therefore of a nervous system 

 which, existing for a few days, might act as a normal reflex centre in the 

 entire absence of the nucleated cell bodies. 



This conception has been realised by Bethe in an experiment in the crab (Carcinus 

 menas). In this animal the reflex movements of the tentacle are carried out by a gang- 

 lion situated at its base. As in the other Crustacea, the cell bodies in this ganglion lie 

 outside the mass of neurofibrils in the centre, forming a sort of capsule (Fig. 152). 

 Bethe was able, under the dissecting microscope, to remove the cell bodies without 

 interfering with the nerves entering or leaving the central mass of fibrils. All the 

 nerve processes with their connections were therefore left intact. In animals, operated 

 in this way, Bethe found that for two or three days the tentacle reacted normally to 

 stimuli applied to its surface. The reflex functions of the ganglion were not in any 

 way affected by the removal of the nucleated bodies of the cells. A similar experi- 



