44 
11. — The Work of Muscle and the Influence of Tension. 
It is well known that the work done by muscle increases, 
up to a certain point, with the magnitude of the load, and 
then decreases to zero, or even becomes negative, in contrac- 
tion. The reason for the initial increase in the work done, 
as well as the cause of the favourable effect of moderate ten- 
sion upon all contractile tissues, lies in the fact that ihe 
tension increases the surface of contact between the hyalo- 
'plasm and spongioplasm. It is, indeed, obvious, a priori, that 
when an elastic substance is stretched in any way its surface 
is increased ; and this is just the case with the sarcous de- 
ments. Hence, the work which has to be done against the sur- 
face tension, along the contact surface, in order to increase 
that surface, is diminished ; and, since the same work as before 
will be done by the ions set free on excitation, only ao^ai^st 
a tension that has been diminished, the output of work will 
be greater. 
At the same time, the longitudinal stretching of the sar- 
cous element (spongioplasm) will have a horizontal compon.^nt 
tending to decrease its diameter — that is, to decrease the elas- 
tic reaction outwards, and so decrease the tendency of the 
sarcous element to bulge on stimulation ; when this unfavour- 
able influence exactly balances the favourable, the work will 
be the same as with a minimal load ; between these points 
there must be a point of maximum work output ; afterwards 
the work falls, and, finally, becomes zero. If, now, more 
loading is added, when the muscle is stimulated, what hap- 
pens is that the pull of the hyaloplasm upon the wall of the 
sarcous element is diminished ; normally the horizontal reac- 
tion would cause the walls to bulge, but now, owing to the 
great vertical strain, the horizontal reaction is converted 
into a vertical one, and the muscle elongates irhen it con- 
tracts: this is known as Weber's paradox.* It is just as if 
one violently compressed an indiarubber tube which was 
being at the same time violently pulled. On releasing the 
compression the tube will become more stretched, and its aver- 
age bore diminished ; but, if the tube were not stretched its 
average bore would be increased. 
12. — The Action of Chemical Reagents upon the 
Contracture of Muscle. 
If the "negativity" at any point in a muscle is deter- 
mined by the number of free kations in the hyaloplasm at 
that point, we should expect to find that when a muscle is 
* Halliburton : Handbook of Physiology, fourth ed'tion, 
page 13/5. 
