152 GENERAL PROPERTIES OF LIVING TISSUES 



horizontally. Bring the writing point against the 

 drum. Light a Bunsen burner. Heat a wire, 

 and kill the pelvic end of the muscle by laying 

 the hot wire against it. Bring one non-polar- 

 izable electrode upon each end of the muscle. 

 Arrange the pole-changer so that the cathode 

 shall be at the pelvic end, and the current there- 

 fore " atterminal," i. e. directed toward the 

 "thermal cross-section." Close the simple key. 



No contraction, or a very slight contraction, 

 will be seen. 



Open the key. Ee verse the pole-changer, so 

 that the current shall be " abterminal." Close 

 the simple key. 



The ordinary closing contraction will be seen. 



The great difference here shown between the 

 polar excitability in the uninjured and injured 

 region is probably due to chemical changes in 

 the injured part. Similar results can be obtained 

 by painting the end of the muscle with one per 

 cent solution of acid potassium phosphate. The 

 irritability is lessened by this salt, but returns to 

 normal if the altered end of the muscle is bathed 

 in 0.6 per cent sodium chloride solution. 



Sodium carbonate has an effect opposite to that 

 of the potassium salts. 



Wet the pelvic end of a fresh muscle with one 

 per cent solution of sodic carbonate. After a 



