86 DYNAMICS OF LIVING MATTER 



irritability. This loss of contact irritability of the muscle in air, oil, etc., 

 may be due to the migration of Ca-ions from the interior of the fiber 

 or muscle to the surface, thus reestablishing approximately the original 

 normal surface condition. If we then put the muscle back for a short 

 time into a sodium citrate or sodium fluoride, etc., solution, a diminu- 

 tion of Ca-ions will again occur in the surface layers, and the contact 

 irritability will be reestablished. As we should expect, the length of 

 time that the muscle remains in the solution is as important as the 

 concentration of the solution. If we dip a muscle for a few seconds 

 only into a sodium citrate solution (i-g. molecule in lo 1.) the 

 contact irritabihty cannot be produced, as there is not time for a large 

 enough number of citrate-ions to enter the muscle. 



Dr. Zoethout carried these investigations still farther. He found 



that if a muscle be put into a pure ^ solution of any potassium salt, 



o 



e.g. KCl, KNO3, KI, KjS04, K-oxalate, etc., the tone of a muscle 



increases, i.e. the muscle shortens while it is in the solution. If, however^ 



the muscle is put into a pure -r CaCl^ or NaCl solution, it again relaxes.* 



o 



The minimum concentration of KCl for bringing about this increase 

 in tone of the gastrocnemius of a frog was i c.c. — KCl + 9 c.c. HjO or 



o 



-^ glycerine. If, however, a potassium salt was chosen whose anion 

 o 



is liable to decalcify the muscle, the minimum concentration could be 



less. Thus \ c.c. — K-citrate -f- 9 J c.c. H3O was already effective, 

 o 



Zoethout interprets this as showing that the Ca-ions of the muscle itself 

 are liable to antagonize the shortening action of the K-ions. This 

 interpretation he supported by a number of experiments. "It occurred 

 to me that since potassium increases the tone of the muscle and calcium 

 inhibits this action of the potassium, it might be possible that the pre- 

 cipitation of the calcium salts causes contact irritability, becauses it 

 destroys the normal equihbrium between these two salts in the muscle." 

 " Upon testing this view we found it to be correct. The contact reaction 

 produced by sodium citrate is increased if we previously, or simul- 

 taneously, introduce K-ions into the muscle. " f Zoethout's conclusions 

 are as follows: "If the calcium salts in the muscle are decreased, the 

 efl&ciency of the K-ions to increase the tone of the muscle is increased. 

 If the K-ions in the muscle are increased, the efficiency of such salts 

 as Na-oxalate and Na-citrate to cause contact irritability is increased. 



* Zoethout, Am. Jour. Physiology, Vol. 7, p. 199, 1902. 

 t Zoethout, Am. Jour. Physiology, Vol. 7, p. 320, 1902. 



