BY DR. MICHAEL FOSTER. 375 



is because the inertia of the needle prevents its responding 

 with sufficient rapidity to the variations in the current. 



The proof that the negative variation of tetanus is thus 

 really made up of a succession of variations is supplied not by 

 the galvanometer, but by the above experiment with the frog's 

 muscle, or, as it is often called, the " rheoscopic frog." 



The above observation will frequently fail unless the nerves 

 are perfectly fresh and irritable. 



06s. IX. Satisfactory results having been obtained, liga- 

 ture tightly in one case the nerve of B between the muscles 

 and the electrodes, and in another the nerve of A between its 

 muscles and the part of the nerve lying on the muscle of B. 



In either case, the secondary contraction in A should be 

 entirely absent. If they are present, they are due to an escape 

 of the current ; and the observation must be repeated on fresh 

 muscles and nerves, greater precautions being taken to pre- 

 vent the escape of the current. 



Obs. X. During contraction, muscle becomes acid. 



Prepare two muscles, either the gastrocnemius or rectus, or, 

 perhaps better still, take the whole of the thigh muscles. 

 Leave one, A, alone ; tetanize the other, B, repeatedly. Make 

 an incision through each and test their reaction. 



A will be found to be neutral or alkaline ; B will be found to 

 be distinctly acid. 



Obs. XL During contraction, the temperature of the mus- 

 cle rises. 



Prepare a whole leg with sciatic nerve ; choose a large, 

 healthy, strong frog. From the thigh resect the femur in its 

 middle for the greater part of its length, injuring the nerve 

 and muscles as little as possible. 



In place of the removed femur, place the bulb of a thermo- 

 meter reading one-tenth of a degree centrigrade at least ; wrap 

 the muscles carefully round the balb ; surround the thigh with 

 cotton-wool, and wait till the level of the mercury is constant. 

 The thermometer should be fixed very firmly and steady. Now 

 send an interrupted current through the nerve. The muscles 

 will be thrown into tetanus, and the mercury in the thermo- 

 meter will rise. 



(For determining more exactly the changes of temperature 

 in a muscle during contraction, it is better to use thermopile 

 needles with a galvanometer of little resistance (see Chap. 

 XVIII., p. 344) ; or for still finer observations, in which it is 

 desirable to avoid the effects of friction, the swinging appa- 

 ratus of Heidenhain may be employed. (See Heidenhain- 

 Me.chan. Leistung, WarmeentvrickelUng^ etc., bei der Muskel- 

 th'dtigkeit.} 



