( 651 ) 
At any rate the question possesses the merit of actuality, and 
I intend trying to elucidate it more fully afterwards. | 
All that has been said here about the muscle-contraction, may be 
said to apply also, with a slight alteration, to the course of the 
one-phased action-current of muscle and nerve, which possesses 
likewise a latent period. 
Ad. IT. With formula (8) the case is far less doubtful. In this 
formula is expressed the effect of a biological constant stimulus. 
The effect is formed by three components. Of these three the first 
term expresses the ever-diminishing magnitude of the effect, if 
no assimilation takes place. The initial magnitude therefore is A. As 
the final magnitude is represented by C, it follows B = — C, and the 
formula is altered to: 
PS Aes RA Se ec RN 
In this formula the first term may be considered as dissimilation 
or exhaustion-term, whilst the second represents the assimilation- or 
restoration-term. 
Therefore we may call « the dissimilation and @ the assimilation- 
modulus. 
Both these moduli are constants only in a mathematical sense, 
i. e. for each special case of stimulation. They may be different 
however for each succeeding case of stimulation. 
The whole of the effect is moreover still dependent on the magnitude 
of stimulus, in the manner explained in our former communications. 
We may therefore add still another factor to formula (14), obtain- 
ing then finally, as a complete representation of the relation between 
magnitude of stimulus, time and effect : 
P= fl—e rk) A et + B(l—e-*)}. ot (15) 
For very small particles of time the second factor in (15) is 
transformed into A, and we again obtain our original law about the 
relation of stimulus and effect, which indeed, as is proved now, 
prevails only where instantaneous stimuli are concerned. Other- 
wise after a brief space of time the influence of assimilation and 
dissimilation will make itself felt. 
As we remarked before, the moduli a and 6 are magnitudes, 
differing for each particular case. The more or less rapid appearance 
of fatigue will be dependent, amongst other causes, on the effect 
or perhaps directly on the magnitude of stimulus. Very often 
however there will occur circumstances, exerting their influence 
on the magnitude of effect, independent of the magnitude of stimulus, 
e.g, the temperature of or the weight lifted by a muscle. 
