694 STUDIES IN GENERAL PHYSIOLOGY 
minute, the muscle will show a slight contraction when 
taken out of the solution. If the process be repeated, a 
stronger contraction will follow when the muscle is removed, 
and after a series of submersions have occurred the muscle 
will give one or a series of powerful contractions every time 
it is taken out of the solution and brought into contact with 
air. After a certain time, which may be an hour or more, 
and which varies according to the solution, the reaction 
becomes weaker and finally ceases. 
If we use a stronger concentration than 1 gram-molecule 
in 8 liters, we get more powerful contractions, but the irri- 
tability of the muscle disappears sooner. 
II. THE NATURE OF THE SOLUTIONS WHICH PRODUCE CONTACT- 
IRRITABILITY IN MUSCLE 
Solutions of cane-sugar or urea were unable to produce 
the contact-reaction in muscle. I have tried these solutions 
in all concentrations from 0 to normal or even 2n. A large 
number of electrolytes were then tested. None of the salts 
of Li, K, Ca, Mg, and NH, gave rise to the contact-reaction. 
This statement is based upon experiments with LiCl, Li,SO,, 
Li,CO,, KCl, K citrate, K oxalate, MgCl,, MgSO,, NH,Cl, 
(NH,),CO,, and ammonium citrate. The degree of dilu- 
tion used was as a rule 1 gram-molecule in about 8 or 10 
liters. In some instances stronger solutions were tried, but 
with the same negative result. 
In my experiments on rhythmical contractions I have 
shown that the sodium ions have a specific réle in the pro- 
duction of these contractions. It seemed also possible that 
they play such a réle in the production of the contact-irrita- 
bility. But I found that or even stronger solutions of 
8 
NaCl, NaBr, NaI, NaNO, did not bring about the contact- 
1Zoethout showed later in my laboratory that the addition of a trace of potas- 
sium citrate to the sodium-citrate solution facilitates the production of contact- 
irritability. [1903] 
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