698 STUDIES IN GENERAL PHYSIOLOGY 
were repeated in an almost pure atmosphere of CO, 
instead of air and the contact-reaction was as powerful 
as in air. 
A second change is the sudden evaporation of water from 
the surface of the muscle upon its leaving the solution. 
The following experiment might suggest that this evapora- 
tion is the cause of the contact-reaction. If we pack a 
muscle, that gives powerful contact contractions, tightly in 
moist filter paper the reaction will not occur when the muscle 
is taken out of the solution, but will occur when the filter 
paper is removed. Nevertheless, evaporation has nothing to 
do with the reaction. We get the contact-reaction quite as 
well in a moist chamber as in dry air. Furthermore we get 
the reaction if we bring the muscle directly from the sodium- 
citrate or fluoride solution into oil, without exposing it to 
air. We can make this experiment in the following way. 
The lower half of the dish, D (Fig. 162), is filled with the 
effective sodium-citrate solution, the upper half with oil 
(I used sperm and olive oil). The muscle is first brought 
into the sodium-citrate solution and then, by lowering the 
support 8, into the oil. Powerful contractions occur. Evap- 
oration of water from the surface of the muscle is, there- 
fore, not the cause of the contractions. 
After this had been established it was to be expected that 
changes in temperature were not responsible for the contact 
reaction. Experiments in which the muscle was rapidly 
cooled and heated yielded only negative results. 
The next possible cause to be considered was electricity. 
The fact that a change from the salt solution to a non-con- 
ductor (air, oil) caused contractions suggested the possibility 
that these contractions were in reality electrical break con- 
tractions, the muscle itself acting as a battery. The only 
fact which did not seem to accord with this explanation was 
the lack of a make contraction when the muscle was put into 
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