702 STUDIES IN GENERAL PHYSIOLOGY 



left column of the above list to those of the right column. 

 But it is obvious too that as soon as this change occurs the 

 surface layer gradually undergoes an alteration, for example, 

 in air, sugar solution, NaCl solution, etc. This change, in 

 which the contact-irritability is lost, occurs most rapidly in 

 a CaCl 2 solution. This suggests the following possibility. 

 The loss of contact-irritability of the muscle in air or oil, 

 etc., is due to the migration of Ca ions from the interior of 

 the fiber or the muscle to the surface, thus re-establishing 

 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 diminution of 

 Ca ions will again occur in the surface layers and the con- 

 tact-irritability will be re-established, As is to be expected 

 the time 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 (1 gram- 

 molecule in 10 liters) the contact-irritability cannot be pro- 

 duced, as there is not time for a large enough number of 

 anions to diffuse into the muscle. 



Still another fact harmonizes with our assumption. If we 

 lift only a piece of the muscle out of the sodium-citrate 

 solution, not the whole muscle contracts, but only the in- 

 dividual fibers that come in contact with the air. Similarly 

 a more powerful contraction occurs when we lift the thick 

 femur end of the gastrocnemius out of the solution than if 

 we expose the thin tendon-Achilles end to the air. 



Finally it should be mentioned that the latent period is 

 somewhat long in these experiments. I have not measured 

 it yet exactly; but it may be a considerable fraction of a 

 second, especially when the contact-irritability is about to 

 disappear. This somewhat long latent period would harmo- 

 nize well with the assumption of contact-phenomena. 



Although I have spoken chiefly of the diminution of 



