Muscuuar TwitcHInes 761 
of the solutions is first brought in contact with the feet 
of the frog. If the feet are not withdrawn, the next 
stronger solution is used, and, if no reaction occurs, the next 
stronger. If one thus succeeds in keeping the feet of the 
animal for one minute or more in the AlCl, solution, subse- 
quent contact of the feet with common tap-water or distilled 
water makes the animal act as if the water caused the most 
excruciating pain. The feet are violently withdrawn, rubbed 
against each other in a way that one notices otherwise only 
when the feet are dipped into strong acids. Ifthe AlCl, 
solution chosen is too strong, the animal will not leave his 
feet in the solution, but will try to withdraw them. But in 
that case its attempts at withdrawing its feet from the solu- 
tion are never as violent as the subsequent attempts at with- 
drawing the feet when brought into contact with common 
water. The stronger the solution of AlCl, is in which the 
feet had been kept, and the longer they had been kept in 
the solution, the stronger their sensitiveness toward water 
will become. 
Sodium citrate acts very similarly to aluminium chloride. 
As the latter is slightly acid and sodium citrate slightly 
alkaline, the possibility was suggested that the H and HO 
ions are responsible for the hypersensitiveness. While it is 
possible to produce occasionally a slight hypersensitiveness 
toward common water by a pure solution of NaOH or HCl, 
the results are very unreliable. It is practically the same if 
one tries to use NaCl solutions to which slight and varying 
quantities of HCl or NaOH have been added. Better results 
can be obtained with solutions of oxalates, sulphates, car- 
bonates, and phosphates. The sodium salts are preferable 
to the potassium salts, for the animal withdraws its feet 
much more rapidly from the solution of a potassium salt 
than from the solution of the corresponding sodium salt. 
This makes it difficult in the case of potassium salts to 
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