696 STUDIES IN GENERAL PHYSIOLOGY 
alkalinity of a sodium formate and sodium valerianate solu- 
tion by adding a small amount of free formic or valerianic 
acid (without, however, rendering the solution entirely 
neutral) they no longer produce the contact-irritability in 
muscle. A small amount of alkali added to a NaCl solu- 
tion may or may not produce a slight degree of contact- 
irritability. 
The solubility of CaSO, is comparatively high, and we 
therefore cannot expect Na,SO, to be very effective for the 
production of contact-irritability. In solutions of 1 gram- 
molecule Na,SO, in 10 liters or less, I sometimes got and 
sometimes failed to get the contact-reaction. May it not be 
possible that the amount of free Ca ions in the muscle of 
a frog varies at different periods of the year, and may not 
this fact account for the seasonal variation in the irritability 
of these animals? But if a Na,SO, solution fail to produce 
contact-irritability in a muscle an addition of some HO ions 
will produced the desired effect. As arule 4 cc. .% LiHO 
or any other hydrate to 100 c.c. of the Na,SO, solution is 
the optimum. We can produce the contact-reaction also 
through the addition of a small amount of acid to the 
Na,SO, solution, e. g., 4 c.c. of #", HNO, (or any other in- 
organic acid) to 100 c.c. of the Na,SO, solution. The effects 
are not so strong as if we add alkali. 
The sulphates showed an exceptional behavior in still 
another direction. With one exception only sodium salts 
give rise to contact-irritability and this exception is a 
sulphate, namely (NH,),SO,. It would almost seem that 
the sulphates have physiological effects aside from their 
effect upon calcium. This is in harmony with Miss Moore’s 
experiments, in which she found that sulphates are as cap- 
able of antagonizing the poisonous effects of a pure NaCl 
solution as calcium salts.' 
1 Moorz, American Journal of Physiology, Vol. V (1901), p. 87. 
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