ABNOKMAL IRRITABILITY PRODUCED BY SALTS 701 



Relaxation of the contracted muscle will occur when the 

 muscle passes from any medium in the right column above 

 to any medium in the left column. 



After the muscle has been treated for some time with any 

 of the efficient solutions (Na citrate, etc.) the contractions are 

 also produced when the muscle passes: 



From f or | sugar solution to air 

 From g or | glycerin to air 

 From any salt solution to air 



A very interesting and theoretically important fact is that 

 the muscle loses this particular form of irritability very soon 

 when it remains in contact with the air, oil, sugar solution, 

 glycerin, or salt solutions different from those that produce 

 this specific irritability. In LiCl or NaCl solutions the 

 contact-irritability is lost as fast as, if not faster than, in a 

 sugar or glycerin solution. We can re-establish the irrita- 

 bility, however, if we put the muscle back into the sodium- 

 citrate solution for some time. This fact, together with those 

 mentioned before, suggests the following as the most prob- 

 able explanation of the peculiar phenomena of contraction 

 with which we have been dealing : the solutions which pro- 

 duce the contact-irritability possess anions that are liable to 

 form insoluble calcium compounds. They are all with one 

 exception (NHJ 2 SO 4 Na salts. Whatever the effects 

 of these anions may be, the fact that in less than a minute 

 the contact effects are noticeable indicates that only the sur- 

 face layer of the muscle or, what is less probable, the surface 

 layer of each individual fiber, is altered. It is impossible for 

 the anions to migrate deeper into the muscle in so short a 

 time. In the surface layer of the muscle or the individual 

 fibers we have temporarily a diminution of Ca ions. We 

 have, then, a muscle, whose surface layer differs from that of 

 an ordinary excised muscle. If this layer is once established 

 the muscle contracts at any change from the media of the 



