2 12 
Mr. Home's Lecture 
object intended by such structure, but rather to procure the 
effect by means of short contractions, which are less fatiguing, 
or in some other way more in the management of the consti- 
tution, than long ones. 
That long contractions in a muscle cannot be supported for 
any length of time, may be illustrated from the actions both 
of the voluntary and involuntary muscles. 
While the voluntary muscles are under the command of the 
will, we cannot ascertain what would be the effects produced 
by the continuance of their contractions, since the influence of 
the brain communicated by the nerves becomes soon weakened, 
and puts a stop to their action ; but when the contractions of 
voluntary muscles are by any circumstance rendered involun- 
tary, the difference in the time of their continuance appears 
to be in the inverse proportion of the quantity of contraction ; 
for muscles, whose usual functions consist in short contrac- 
tions, can go on for a long time, while those which are per- 
formed by long contractions soon cease. 
In the muscles of a paralytic arm, their action, to a certain 
extent, is continued for years (the times of sleeping excepted), 
without any effect being produced upon the constitution, or 
the parts themselves ; but in epileptic fits, in which the actions 
are equally involuntary, only requiring longer contractions, 
they soon cease, leaving the person greatly exhausted ; an ef- 
fect which must arise from the quantity, not the frequency, of 
the contractions. 
If we attend to the actions of the involuntary muscles, we 
find that they are continued through life, but that the quan- 
tity of contraction is very small ; and if from any circumstance 
the quantity should be increased, it cannot be continued, the 
