PHYSICS OF THE BRAIN. 
42* 
artificial states in which its functions have been suppressed. 
But we are led also to another subject, I mean the natural iner- 
tia or rest of the brain, which we call sleep. Physically the 
brain asleep is the brain exhausted of its force — force expended 
during waking hours in the production of its equivalent of 
animal motion. As the sleep creeps on, the natural imagery 
of brain rests. During sleep, motion being suspended, the 
brain and nervous centres altogether are recharged, and natural 
awaking is the index of the fact. 
But it is not always that the brain centres rest as a whole, or 
work as a whole. Sometimes one part of the brain works while 
the rest sleeps, and then we dream in sleep, sleep being the major 
phenomenon. Carmichael, many years ago, well taught that 
there are seven distinct stages of waking and sleeping. 1 . When 
the entire brain and nervous system are buried in sleep , then 
there is total exemption from dreaming. 2. When some of the 
mental organs are awake , and all the senses are asleep , then 
dreams occur and seem to be realities. 3. When the above con- 
dition exists , and the centres of voluntary motion are also 
awake , then may occur the rare phenomenon of somnambulism. 
4. When one of the senses is awake with some of the mental 
organs , then, during our dream, we may be conscious of its illu- 
sory nature. 5. When some of the mental organs are asleep , 
and two or more senses awake , then we can attend to external 
impressions, and notice the gradual departure of our slumbers. 
6. When we are totally awake and in full possession of our 
faculties and powers. 7. When , under these circumstances , we 
are so occupied ivith mental operations as not to attend to the 
impressions of external objects, then our reverie deludes us like 
a dream. These are faithful observations, and define with ex- 
actitude the fluctuations of force in the brain under different 
conditions. In experimental research, and in disease, we have 
the same phenomena brought before us, and they all accord as 
to cause. 
Intoxication. 
There are various modes of producing insensibility artificially. 
The insensibility of intoxication from alcohol is an illus- 
tration at hand. The insensibility thus produced is the same 
as that from cold ; the agent taken, that is to say, interferes 
with the distribution of force through the brain substance, and 
is carried away at the expenditure of so much force as shall be 
required for its elimination. At the late meeting of the British 
Association for the Advancement of Science at Dundee, I showed 
that the period of action of alcohols of different kinds could 
be determined by the force required to lift them out of the 
organism. Moreover, various of these intoxicating substances, 
