470 PHYSIOLOGY CHAP. 



produced by alcohol, ether, chloroform, or chloral hydrate. Yerworn 

 and his pupils showed that narcotics disturb oxidation in the 

 nerve-cells, even when these cells are in extreme need of oxygen, 

 as when fatigued, and they become unable to assimilate it. In 

 sleep, on the contrary, the conditions are diametrically opposite to 

 those of narcosis ; it is by means of oxidative processes that the 

 nerve-cells recover, and that the excitability of the system 

 gradually rises to the level of the waking state. 



Neither the fatigue of the ganglion cells in the waking state 

 which predisposes to sleep, nor their recovery and recuperation 

 during slumber, are, however, a sufficient basis for an adequate 

 theory of the origin of sleep or awakening, although they express 

 the nature of these in general and result physiologically from one 

 or the other phase of daily life. 



More prominence has, unfortunately, been given to the so- 

 called histological theory of sleep, which is founded on the supposed 

 amoeboidism or mobility of the neurodendrites. Among the 

 supporters of this theory are Eabl-Euckhard, Lepine, M, Duval, 

 and Lugaro. 



Lepine (1895) assumed that sleep was due to a retraction of 

 the central terminations of the sensory neurones, and thus to their 

 isolation from the neighbouring neurones ; waking, on the contrary, 

 being the result of re-established interneuronic contact. This, in 

 his opinion, explains the instantaneous onset of and recovery 

 from sensory or motor paralysis in certain hysterical subjects, and 

 the fact that many normal persons can pass instantaneously from 

 the waking to the sleeping state, and vice versa. 



" In sleep/' writes Duval, " the cerebral ramifications of the 

 central sensory neurone are retracted, like the pseudopodia of an 

 anaesthetised leucocyte, owing to absence of oxygen and excess of 

 carbon dioxide. Feeble excitations of the sensory nerves provoke 

 reflex reactions in the sleeper, but do not affect the cortical cells. 

 Stronger stimuli provoke elongation of the cerebral ramifications 

 of the central sensory neurones, and consequently the stimulus 

 passes to the cortical cells, and the subject awakes." 



.This amoeboidism of the neurodendrites is not, however, 

 founded on any positive observation, and was not accepted by 

 Eamon y Cajal and Kolliker, the principal authorities on this 

 subject, and the founders of the neurone theory. No amoeboid 

 movement is visible, according to Kolliker, in the terminal 

 appendages of the nerve-fibres, when these are observed in 

 transparent parts of living animals. The axis-cylinder termina- 

 tions of different nerve-organs present, according to Cajal, the 

 same mode of connection by their respective dendrites in animals 

 killed by chloroform or by bleeding or by poisoning, in such as 

 were kept for a long time in rest or darkness, and in those fatigued 

 before killing them. 



