1910.] 



The Origin o f Osmotic Effects. 



599 



water into certain regions, giving rise to local expansions which determine 

 the shortening of the fibres ; but when the osmotic tension within the cell is 

 raised by these to a certain maximum, an increase of the excitant would 

 tend to determine an outflow rather than an influx of fluid ; at this stage 

 electric stimulation would have little effect. 



The argument may even be extended to the explanation of the phenomenon 

 of narcosis in general, including sleep. In saying this, we are aware that 

 physiologists have deprecated the comparison of sleep with the condition 

 induced by anaesthetics. Thus, according to Halliburton,* " the sleep of 

 anii'Sthesia is a pathological condition due to the action of a poison. The 

 drug reduces the chemico-vital activities of the cells and is, in a sense, 

 dependent on an increasing condition of exhaustion, which may culminate in 

 death. Normal sleep, on the other hand, is not produced by a poison or at 

 any rate we have no evidence of any poison ; it is the normal manifestation 

 of one stage in the rhythmical activity of nerve-cells and though it may be 

 preceded by fatigue or exhaustion it is accompanied by repair, the construc- 

 tive side of metabolic activity." 



But such statements raise many questions. It may be asked : What is 

 a poison ? How does a poison act ? What are chemico-vital activities ? 

 These must be answered before it can be asserted that sleep is not produced 

 by a poison. It has been observed that in deeply anaesthetised animals the 

 dendrites of the nerve-cells exhibit thickenings or moniliform swellings ; 

 hence it has been inferred — to quote Halliburton (p. 740) — that " in the 

 waking state, the neighbouring nerve units are in contact with each other ; 

 transmission of nerve impulses from neuron to neuron is then possible and 

 the result is consciousness ; during sleep the dendrites are retracted in an 

 amoeboid manner ; the neurons are therefore separated and the result is 

 unconsciousness." 



Suppose that a poison such as hydrogen cyanide were to penetrate rapidly 

 into the nerve-cells, such swellings might well take place in the main body 

 of the cell and elsewhere, in consequence of the influx of water conditioned 

 by the presence of the " poison " within the cells ; in elongated cells this 

 influx would cause a reduction of length along the major axis and might 

 well determine the retraction of the dendrites. Such a messenger 

 (Hormone) would interrupt communication in the nervous system instead of 

 promoting it. 



Fatigue diminishes the readiness of the central nervous system to respond 

 to nervous stimuli ; presumably, however, fatigue is conditioned not merely 

 by the exhaustion of the supply of changeable material but is also conse- 

 * ' Physiology,' 9tli edition, 1909, p. 742. 



