SECTION V 

 FUNCTIONS OF THE NERVE-CELL 



WHEN a unicellular organism, containing a single nucleus, is cut into 

 two parts, both continue to live for some time, each performing 

 active movements and evincing all the phenomena which we 

 associate with activity and therefore with destructive katabolism. 

 For the continued existence of a cell the processes of constructive 

 metabolism, or anabolism, must take place pari passu with those 

 of disintegration, and for this the presence of the nucleus is 

 necessary. Hence, in a few days, the half cell with the nucleus 

 has repaired its loss and become once again a normal individual, 

 whereas the half without a nucleus undergoes degeneration and 

 death. The axon of a nerve- cell can be regarded as analogous to a 

 long pseudopodium of an amoeba. Like this, if cut away from that 

 part of the cell containing the nucleus, though capable for a time of 

 discharging its active function of propagation of excitatory impulses, 

 yet it finally dies, death of the nerve fibre occurring in the mammal 

 within three to five days after separation of the axon from the cell. 

 Every nerve- cell therefore may be looked upon as a trophic centre 

 of the nerve fibre proceeding from it as well as of the medullary 

 sheath, which is practically a product or secretion of the axis 

 cylinder. But has the nerve-cell any more important functions to dis- 

 charge ? It has long been customary to endow 7 the nerve- cell with all 

 the properties which are distinctive of a nervous system, and to 

 ascribe to it the active part in the origination of automatic actions, 

 in the reflection of afferent impulses, and in the supply of energy to 

 all nervous processes. That the passage of impulses through the nerve- 

 centres requires the expenditure of energy by these centres can be 

 proved in various ways. In the first place, we have the fact that in 

 all nervous systems, at any rate of the higher animals, arrangements 

 are made for their free supply with oxygen. Very short deprivation 

 of oxygen causes a complete block throughout the system, in many cases 

 preceded by a short period of increased excitability or ease of trans- 

 mission. If, in the rabbit, the thoracic aorta be clamped for a few 

 minutes, the hind limbs become paralysed, and if the obstruction be 

 continued for half an houp, here is widespread degeneration and death 

 of the cells with their fibres in the grey matter of the lumbar and 



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