APPLICATIONS OF THE GRAPHIC METHOD, 181 
tively slow, then more rapid, and again slower, till a brief sta- 
tionary period is reached, when the muscle gradually but rap- 
idly returns to its previous condition, passing through the same 
phases as during contraction proper. In other words, there is 
a period of rising and of falling energy, or of contraction, and 
relaxation. 4. A period during which invisible changes, as 
will be explained later, are going on, answering to those in the 
nerve that cause the molecular commotion in muscle which 
precedes the visible contraction—the latent period, or the 
period of latent stimulation. 
The facts may be briefly stated as follows: The stimulation 
of a muscle either directly or through its nerve causes contrac- 
tion, followed by relaxation, both of which are preceded by a 
latent period, during which no visible but highly important 
molecular changes are taking place. The whole chain of events 
is of the briefest duration, and is termed a muscle contraction. 
The tracing shows that the latent period occupied rather more 
than z4, second, the period of contraction proper about 74, 
and of relaxation $5 second, so that the whole is usually begun 
and ended within ~, second; yet, as will be learned later, 
many chemical and electrical phenomena, the concomitants of 
vital change, are to be observed. 
In the case just considered it was assumed that the muscle 
was stimulated through its nerve. Precisely the same results 
would have followed had the muscle been caused to contract 
by the momentary application of a chemical, thermal, or me- 
chanical stimulus. 
If the length of nerve between the point of stimulation and 
the muscle was considerable, some difference would be observed 
a bY 
Fia. 179.—Diagrammatic representation of the measurement of velocity of nervous impulse 
(Foster). Tracing taken by pendulum mayperapt (Fig. 177). The nerve of same muscle- 
nerve preparation is stimulated in one case as far as possible from muscle, in the other as 
near to it as possible. Latent period is ab. ab’, respectively. Difference between ab and 
ab’ indicates, of course. length of time occupied by nervous impulse in traveling along 
nerve from distant to near point. 
in the latent period if in a second case the nerve were stimu- 
lated, say, close to the muscle. This is represented in Fig. 179, 
