2i6 SCIENCE PROGRESS 



true of the synapses within the sensory centres in the cortex 

 cerebri, regions which therefore enter on a state of functional 

 rest the psychic correlative of which is the unconsciousness 

 of sleep. The view of Duval ^ and Cajal,^ that the arborescent 

 end of the neurone at the sjniapses retracts in consequence of 

 this poisoning, is extremely difficult of histological demon- 

 stration ; if a fact, it supplies a physical basis for the increase 

 of synaptic resistance. 



It seems clear that there is an insomnia due in excessive 

 fatigue to the very virulence of the toxaemia. The man not in 

 " training " knows well its sj^mptoms : headache, slight nausea, 

 slight fever, feeling of general discomfort which together effect- 

 ively banish sleep. Children frequently exhibit this type of in- 

 somnia, describing it by saying that they are " too tired to sleep." 

 Of course the chemical factor is not alone causal in this case, for 

 the heart is certainly beating faster partly by reason of the 

 fatigue-products circulating through it and partly by reason of 

 the slight increase of temperature of the blood, the fever in its 

 turn being the result of the general toxaemia. The insomnia 

 may be more directly due to the sensations of discomfort from 

 muscles and joints, but the chemical factor in this case is 

 certainly present. This view undoubtedly involves the idea 

 that fatigue-toxins when in slight or what might be called 

 " normal " amount can cause sleep— that is, depress cerebral 

 activity; whereas if in greater concentration they act in the 

 direction of stimulating and so keeping awake the cerebral 

 cells. 



Pharmacologists are quite familiar with similar examples of 

 the difference of action between drugs in small and in higher 

 concentration in the blood. 



That this chemical factor is most potent in sleep-production 

 there can be no manner of doubt, for the fatigue-induced sleep 

 can reach a degree of profoundness of unconsciousness that 

 is exhibited by no other physiological state of the cerebrum. 

 We have authentic accounts of soldiers suffering from the 

 excessive fatigue of forced marches, as in Kitchener's dash on 

 Khartoum, rolling off the camels and falling sound asleep while 

 the rest of the army thundered past. In the coaching days 



' " Hypoth^se sur la physiologic des centres nerveux ; theorie histologique du 

 Sommeil," Soc. de Biol., 1895, p. 85. 



^ Archivf. Anat. u/id F/iys., 1895, Heft 4-6, p. 375. 



