HISTOLOGICAL ELEMENTS 



859 



side of the cell. Certain changes in the neurofibrils of the cell may 

 accompany the changes in the chromatin. In rabbits after division 

 of the facial nerve the alterations in its nucleus of origin have been 

 found to reach a maximum in about three weeks, after which there is a 

 tendency to recovery on the part of the majority of the cells, even when 

 regeneration of the nerve has been prevented by cutting out a portion 

 of it. Some of the cells may completely atrophy and disappear. 

 Similar changes have been found by Warrington in the motor cells ol 

 the anterior horn after section of the posterior (dorsal) spinal roots. 

 Since in this case no anatomical injury has been inflicted on the motor 

 neurons, it has been surmised that the cause of the alterations is the 

 loss of impulses which normally reach them along their dendrites. In 

 short, we may say, with Marinesco, that the functional and anatomical 

 integrity of the neuron depends on the integrity of all its constituent 

 parts, and of the neurons which carry to it functional excitations i.e., 

 excitations connected with its proper physiological work. The neuron, 

 in fact, lives by its function, or, in common language, by doing its 

 work. Yet the anatomical tokens of mere disuse, as in the motor cells 



Fig. 340. Cells from the Nuclei of the Oculo-Motor Nerves of the Cat Thirteen Days 

 alter Division of the Root-Fibres on one Side: Nissl's Stain (Barker, after Flatau). 

 a, normal cell from side on which the roots were not cut ; b, cell from side operated 

 upon. Only a few Nissl bodies are present in b, and the nucleus is displaced to 

 one side of the cell. 



of the anterior horn after division of the cord at a higher level, are less 

 distinct than those which follow section of the axon. Therefore it 

 must be concluded that the latter, although not indispensable for the 

 nutrition of the cell as the cell is for the axon, exerts an influence upon 

 it. Similar changes in the chromatin may also be produced in nerve- 

 cells by a period of anaemia, in extensive superficial burns, in tetanus 

 caused by the injection of bacterial cultures, in acute alcoholic poisoning, 

 in fatigue, and in other ways. According to Wright, the inhalation 

 of ether or chloroform (in dogs) so alters the chromatic substance 

 that it loses its affinity for aniline dyes. In long-continued anaesthesia 

 the nucleus is also affected, while the nucleolus is the last part of the 

 cell to suffer. A greater alteration occurs in the cells in the three hours 

 between the sixth and ninth hours of anaesthesia than in the five hours 

 between the first and sixth. Although the changes are transitory, the 

 cells, after a narcosis of nine hours, being practically normal in forty- 

 eight hours, they indicate that the duration of safe surgical anaesthesia 

 has a limit measured by hours. 



It is probable that the alterations in the chromatic substance should 



