166 
IOWA ACADEMY OF SCIENCE Voi,. XXVIII, 1921 
entire length of the writing arm being 150 mm. from the pivot. 
The kymograph used in recording was of the modified Harvard 
slow driving, long paper type, so provided with a fan that it made 
one revolution in about seventeen, minutes. All records shown 
in the subjoined plates were made with the drum revolving at 
this uniform speed so that from this factor they are comparable. 
During the experimentations care has been exercised to keep 
the various mechanical and thermal conditions as constant as pos- 
sible ; the temperature has not been allowed to fluctuate more than 
two degrees, at any time, usually the room temperature being kept 
as approximately 21 °C. during all the experiments. The various 
concentrations of fluids used were made up in advance according 
to computed volumes per cent, and placed in small cork stoppered 
flasks of 150 cc. capacity so that at the time of experimentation 
they were approximately at room temperature. The manner of 
attachment of the muscle to the electrodes was carefully ob- 
served, and consisted of inserting the needle in the tendon achilles 
just at the junction of the fascia of the numerous muscle bundles 
for the lower contact; the upper end of the muscle being made 
secure by piercing the tendonous fascia at the knee joint between 
the distal end of the femur and the proximal end of the tibia. 
This precaution to make secure the electrodes was found to be 
imperative since otherwise the inertia of the falling weight on the 
writing lever opposing the muscle would invariably alter the elas- 
ticity of the muscle and complicate the curves, especially in the 
initial excursions of the lever. 
By closing the short circuit bar on the key, the interrupter in 
the primary circuit activates ® intermittently the signal magnet and 
at the same time sends the make and break shocks to the muscle 
through the inductorium. It is assumed that by keeping constant 
the relative positions of the primary and the secondary coils the 
resulting successive induced shocks which reach the muscle will 
be approximately of the same strength throughout any series of 
experiments. This factor, of course, is a very important one 
since the responses of skeletal muscles when applied with grada- 
tions of current are markedly affected in a number of its phases, 
especially fatigue, as has been recently shown by Pratt®. Assum- 
ing the factors just mentioned to be fairly constant throughout 
the series of experiments to be described, there is yet another 
variable not easily controlled, that of metabolic variability in the 
individual muscles. Equality in size and weight of the experimen- 
