( 58 ) 
then again so much acid was added, till a new group of reflex-con- 
tractions appeared. In these experiments the acid in the burette con- 
tained 40 grams of oxalic acid per liter solution. As a measure of the 
stimulus in physical units the concentration of the solution, in which 
the leg was immersed, was chosen. The concentration is defined as 
the proportion between the quantities of oxalic acid and water, while 
as the unity of weight the molecular weight was chosen (126 for 
oxalic acid, 18 for water). 
The result of the experiments was given in a table in the following 
way. The first column gives the concentration of the solution in the 
vessel, just at the moment the leg begins to show a group of 
reflex-contractions. The second column contains the increment, which 
the concentration in the vessel must undergo to produce again a set 
of reflex-contractions. The third column gives the relation between 
this quantity and the absolute value of the concentration at the moment 
that the reflex-contractions appear. This column contains therefore 
the quotient of WEBER. 
Let us now consider in how far this experiment satisfies the con- 
ditions put by the formula. The researches of EckHARD, KOSCHEWNIKOFF, 
C. Meyer and SHERRINGTON have proved, that the same spinal segments 
which innervate the skin of the hind leg, supply also the muscles 
of the leg with nerves. If we have cut the spinal cord at the upper 
end and have therefore annulled the influence of the higher centra, 
we have in the hind leg a segmental primary reflex-apparatus. The 
receptive organs of this reflex-apparatus lay in the skin, while the 
muscle forms the transformer. Adopting the simple law of distribution, 
I record only the mechanical effect. In this respect the experiment 
fulfils the required conditions. 
The interpretation of the mechanical effect is very difficult as 
the new state of equilibrium is not reached at once, but only after 
oscillating round this new state. It is therefore hard to say what 
part of the total effect must be considered as the quantity A / of 
the formula. Fig. I is the reproduction of a typical tracing. After the 
reflex-apparatus is in perfect rest, the tap of the burette is opened at 
the moment indicated in the curve by a couple of vertical small lines 
on the base line and oxalic acid is slowly added under continuous 
stirring. At the moment that the first contraction appears, the tap of 
the burette is closed and no more acid is added. At this moment the 
increase of concentration amounted to 3.210 the initial concen- 
tration being 15.910—5. The curve represents the mechanical effect, 
following upon this increase of the concentration of the acid in the 
vessel. This effect consists of a group of great contractions, followed 
