APPLICATIONS OF THE GRAPHIC METHOD. 909 
The contraction of a muscle, and the passage of a nervous 
impulse, are accompanied by electrical changes. Whether cur- 
rents exist in uninjured muscle and nerve is a matter of con- 
troversy. All physiologists agree that they exist in muscle 
(and nerve) during functional activity. This electrical condi- 
tion is termed the “negative variation” by those believing in 
currents of rest, and the “current of action” by those holding 
opposite opinions, The current is of momentary duration, and 
is manifested during the latent period of muscle, in which also 
the chemical changes take place; so that a muscular contrac- 
tion must be regarded as the outcome of the events of the 
latent period, which is, therefore, though the shortest, the most 
important of the phases of a muscular contraction. 
During the passage of a constant (polarizing) current from 
a battery through a nerve, it undergoes a change in its irrita- 
bility and shows a variation in the electro-motive force of the 
ordinary nerve-current (electrotonus). This fact is of thera- 
peutic importance. The electrical phenomena of nerve are alto- 
gether more prominent than the chemical, the reverse of which 
is true of muscle. The activity of a muscle (and nerve proba- 
bly) is accompanied by the generation of heat, an exaltation of 
which takes place during muscular contraction. 
Rigor mortis causes an increase in temperature and the 
chemical interchanges which accompany the other phenomena. 
A muscle may also become rigid by passing into rigor caloris. 
Living muscle is translucent, alkaline or neutral in reaction, 
and elastic; dead muscle, opaque, acid in reaction, and devoid 
of elasticity, but firmer than living muscle, owing to coagula- 
tion of the muscle-plasma. Dead nerve undergoes similar 
changes. 
The elasticity of muscle is restricted but perfect within its 
own limits. It differs from that of inorganic bodies in that the 
increments of extension are not directly proportional to the in- 
crements of the weight. When overstretched, muscle does not 
return to its original length (loss of elasticity), hence the serious 
nature of sprains. 
It is important to regard muscular elasticity as an expres- 
sion of vital properties. 
The work done by a muscle is ascertained by multiplying 
the load lifted by the height; and the capacity of an individual 
muscle will vary with its length, the arrangement of its fibers, 
and the area of its cross-section (i. e., on the number of fibers). 
The work done may be regarded as a function of the resist- 
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