THE DEEPENING OF PHYSIOLOGY. 307 



(3) A third foundation for the neuron-theory 

 has been afforded, as Verworn points out, by experi- 

 mental work. As early as 1852 Waller showed that 

 a nerve-fibre degenerates when its connection with the 

 associated nerve-cell is severed; Von Gudden, Von 

 Monakow, Ranvier, Forel, and many others have con- 

 tinued the enquiry, and have demonstrated that the 

 cell as well as the fibre suffers when their connection 

 is broken. This points again to the unity of the 

 neuron. 



The last decennium of the nineteenth century has 

 been rich in investigations prompted by the neuron 

 theory. (a) The internal complexity of the nerve- 

 cell and its processes has been disclosed by many 

 different methods ; it is enough to say that the nerve- 

 cell is a microcosm in itself. (&) The difficult 

 question of the inter-relations of adjacent neurons has 

 been much discussed, and although it is certain that 

 the neurons of adult animals have intimate functional 

 inter-relations, it is difficult to make any general state- 

 ment in regard to the exact nature of the contact or 

 continuity, (c) It is necessary to have some hypoth- 

 esis in order to interpret the making and breaking 

 of the conducting paths through the jungle-like com- 

 plexity of the grey matter and many suggestions have 

 been made, discarded, rehabilitated, and again re- 

 jected. In no other way, until an epoch-making dis- 

 covery is made, can there be progress. Thus, Prof. 

 Mathias Duval in his " histological theory of sleep " 

 suggested that the dendrites of the cerebral cortex 

 contract, like the pseudopodia of an Amoeba, when 

 the cell is fatigued, that sleep (with its dislocated 

 consciousness) ensues, and that during the period of 

 rest the dendritic processes stretch out again into 

 contact with their neighbours. The idea that the cells 



