ABNORMAL IRRITABILITY PRODUCED By Sauts 693 
shortening. But as soon as it is taken out of the solution 
and comes in contact with air, it goes into tetanus or per- 
forms a series of powerful contractions. 
The tetanus or the 
contractions cease at once and relaxation of the muscle 
occurs when the muscle is put back into the solution. 
It was found that not only the change of contact from 
the above-mentioned solutions to air but 
also toa number of other media produce " 
these contractions. What the nature of 
the stimulus in this case is I cannot say 
definitely. Provisionally I will assume 
that we are dealing with contact-irrita- 
bility and I will call the above-mentioned 
reaction of the muscle the contact-reac- 
tion. It would seem as though the en- 
trance of the anions of the above-men- 
tioned solutions caused a change in the 
superficial layer of the muscle or its 
individual fibers, either by precipitating 
calcium or by otherwise altering the con- 
stitution of the protoplasm. This change 
is intensified by the increase in Na ions 
al 
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7 
FIG, 162 
in the same layer. In this condition the muscle is sensitive 
to the nature of the substance with which it comes in contact. 
In these experiments one end of the gastrocnemius of a 
frog is tied to a glass rod, G (Fig. 162), and the other end 
is tied to the lever, L. A dish, D, containing the solution 
is raised from below when we wish to submerge the muscle, 
and is lowered when we wish to bring the muscle into con- 
tact with air. 
In order to demonstrate the contact-irritability I used a 
solution of 1 gram-molecule of sodium fluoride or sodium 
citrate, etc., in about 8 or 10 liters. If the fresh gastrocne- 
mius of a frog be put into such a solution for about one 
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