1899] A THEORY OF SLEEP 137 
irrigation cease; my Amazon is dry and the pale brain can drink no 
more from the drained internal stream. ‘True sleep comes then. 
Cadaverous decomposition is, however, accompanied with some slight 
currents which are neither protoplasmic nor co-ordinated. 
About some Particular Cases, 
(a) Trance——This consists in the diminution of certain currents, 
and is.a more limited sleep than that effected in normal conditions. 
Hypnotizers avail themselves of several means of fixing or inhibiting 
currents (compression of the eyes, staring, gazing at a brilliant object, 
or suggestion, that is, the inhibiting action of the will on some nervous 
currents of a particular sort). 
(6) The sleep of nocturnal animals in the course of day is related 
to the action of light. In Mexico bats have been observed to issue 
from their dens during eclipses of the sun; gnats flutter in rooms during 
day-time as soon as all doors are shut so as to leave the apartment in 
the dark. Everyone has seen that owls close their eyelids whenever a 
vivid light strikes them. 
(c) Muscular Relaxation during Sleep—I believe that muscular 
contractions are due to certain changes in the volume of the proto- 
plasmic alveoli. Rhumbler has demonstrated that such is the possible 
cause of mytosis, and that the rows of small alveoli, when these are 
partly emptied, diminish in volume and exercise a strong tension on 
the centrosomes. The dynamical influence of those changes being 
wanting when nerves are sleeping, and there are no waves nor modi- 
fications in the intra-alveolar pressure, it is clear that muscles must 
relax. 
The same happens in several pathological cases under the influence 
of fatigue or of certain depressing emotions, etc. This means that I 
suppose nervous waves to provoke the passage of the alveolar enchy- 
lema into the protoplasm of the muscles either by the mechanical 
action of the shock or by an increase of hydrostatic pressure. I do 
not deny that the latter have the structure and elasticity required. 
It will be remembered that the muscular wave moves along the muscles 
of ants in such a way that it is observable under the microscope. This 
could not be the case in a homogeneous liquid. 
(ad) Naturalists faithful to the old school would find a remarkable 
“harmony ” in the following fact :— 
According to Van Beneden the intestinal worms of bats enter into 
a period of hibernal sleep at the same time as their hosts. That is to 
say that the deep protoplasmic currents are delayed both in the host 
and its parasite by lack of nourishment. 
