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 4 is comparatively high, and we 

 therefore cannot expect Na 2 SO 4 to be very effective for the 

 production of contact-irritability. In solutions of 1 gram- 

 molecule Na 2 SO 4 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 2 SO 4 solution fail to produce 

 contact-irritability in a muscle an addition of some HO ions 

 will produced the desired effect. As a rule 4 c.c. -f- LiHO 

 or any other hydrate to 100 c.c. of the Na 2 SO 4 solution is 

 the optimum. We can produce the contact-reaction also 

 through the addition of a small amount of acid to the 

 Na 2 SO 4 solution, e. g., 4 c.c. of ^ HNO 3 (or any other in- 

 organic acid) to 100 c.c. of the Na 2 SO 4 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 4 ) 2 SO 4 . 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 



1 MOOKE, American Journal of Physiology, Vol. V (1901), p. 87. 



