t is a real companion to Crimson Rambler.--The
Gardeners' Chronicle.

[Illustration: ROSE HYBRID POLYANTHA "PSYCHE"--COLOR, PALE PINK.]

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SLEEP AND THE THEORIES OF ITS CAUSE.

The theory of the origin of sleep which has gained the widest credence
is the one that attributes it to anaemia of the brain. It has been
shown by Mosso, and many others, that in men with defects of the
cranial wall the volume of the brain decreases during sleep. At the
same time, the volume of any limb increases as the peripheral parts of
the body become turgid with blood. In dogs, the brain has been
exposed, and the cortex of that organ has been observed to become
anaemic during sleep. It is a matter of ordinary observation that in
infants, during sleep, the volume of the brain becomes less, since the
fontanelle is found to sink in. It has been supposed, but without
sufficient evidence to justify the supposition, that this anaemia of
the brain is the cause and not the sequence of sleep. The idea behind
this supposition has been that, as the day draws to an end, the
circulatory mechanism becomes fatigued, the vasomotor center
exhausted, the tone of the blood vessels deficient, and the energy of
the heart diminished, and the circulation to the cerebral arteries
lessened. By means of a simple and accurate instrument (the
Hill-Barnard sphygmometer), with which the pressure in the arteries of
man can be easily reckoned, it has been recently determined that the
arterial pressure falls just as greatly during bodily rest as during
sleep. The ordinary pressure of the blood in the arteries of young and
healthy men averages 110-120 mm. of mercury. In sleep, the pressure
may sink to 95-100 mm.; but if the pressure be taken of the same
subject lying in bed, and quietly engaged on mental work, it will be
found to be no higher. By mental strain or muscular effort, the
pressure is, however, immediately raised, and may then reach 130-140
mm. of mercury. It can be seen from considering these facts that the
fall of pressure is concomitant with rest, rather than with sleep. As,
moreover, it has been determined on strong evidence that the cerebral
vessels are not supplied with vasomotor nerves, and that the cerebral
circulation passively follows every change in the arterial pressure,
it becomes evident that sleep cannot be occasioned by any active
change in the cerebral vessels. This conclusion is borne out by the