BY DR. MICHAEL FOSTER. 373 



By contraction, especially by tetanus, irritability of a muscle 

 is diminished; after a period of rest, the irritability returns 

 even in a muscle removed from the blood current. 



Obs. V. Repeat the observation on a muscle still connected 

 with the blood current. The return of irritability will be much 

 more rapid and complete. 



With a Du Bois Reymond's^induction apparatus, the transi- 

 tion from a single induction suock to an interrupted current 

 may easily be effected thus : The apparatus being arranged for 

 an interrupted current, the key a being open, press the spring 

 of the magnetic interruptor up to the platinum point, and open 

 the key b. The current breaks into the primary coil, and a 

 single (making or closing) induction shock is the result. On 

 letting go the spring, an interrupted current is at once ob- 

 tained. This may be stopped at any moment by pressing 

 down the spring, and then a single shock is again obtained 

 by letting it rise once against the platinum point, and keeping 

 it there. 



III. Phenomena Attending Muscular Contraction. 



These can only be satisfactorily determined by studying 

 tetanus. The changes in a single contraction are too slight 

 and transitory to be distinctly appreciated. 



Obs. VI. During contraction there is no appreciable change 

 of bulk. 



Take the whole leg, or, better still, both legs, of a frog, in- 

 cluding the attachment of the thigh muscles to the ilium and 

 coccyx, and remove the skin. Tie a thin platinum wire round 

 each end of the leg. Place the thigh in a bottle filled with 

 normal saline solution, insert a cork in the mouth, bring the 

 platinum wires through the cork, and in the centre of the cork 

 insert a narrow glass tube. Fill the tube up to a certain height 

 with the saline solution, make sure that no air bubble remains 

 below the cork or entangled in the leg, and that the cork is 

 tight. Place a scale behind the glass tube in order that the 

 level of the solution may be exactly determined, and bring the 

 platinum wires into connection with an induction coil arranged 

 for an interrupted current. 



Tetanize the leg with a strong current ; even at the height 

 of the tetanus, no perceptible change of level in the fluid in the 

 tube will take place. 



Obs, VII. During contraction the elasticity of the muscle is 

 diminished^ i. e., its extensibility is increased. 



Load a muscle with 50 grammes, and record the amount of 

 extension. Remove the load and tetanize>tie muscle. At the 

 height of tetanus, load the muscle again with the 50 grammes 

 and record the extension. This will be found to be much 

 larger in the second instance than the first. If tracings of the 

 extension be taken on a revolving cj-linder, curves similar to 



