36 ADVANCED LESSONS IN PRACTICAL PHYSIOLOGY 



this reflex proves that the impulses set up in nerve 2 are conveyed into the spinal 

 cord and from here outward to the muscles of the non-curarized left leg. On stim- 

 ulating either gastrocnemius muscle (3 and 4) a reaction is obtained. This proves 

 that the curare establishes a block between the nerve-fibers and the substance of the 

 muscle, i. e., it paralyzes the motor plates. Secondly, it may be concluded that a 

 muscle which has been isolated in this manner from the central nervous system is 

 still irritable and contractile. Consequently, muscle substance so isolated is capable 

 of acting independently of the nervous tissue. 



2. Irritability and Conductivity. In order to distinguish between 

 these two properties of living substance we usually make use of a nerve- 

 nuiscle preparation which is placed upon a plate, 

 while its nerve is drawn through the openings of a 

 small gas chamber. Pieces of moistened filter-paper 

 are placed flat across these openings. Inside the 

 chamber the nerve rests upon a pair of needle elec- 

 trodes (A), and outside the chamber upon a pair of 

 ordinary platinum electrodes (B). Both pair of elec- 

 trodes are connected with the end-cups of a pole 

 changer. The side cups of the latter are then united 

 with the secondary coil of an inductorium. The inlet 

 tube of the gas chamber is made to communicate 

 with a generator bottle containing pieces of marble. 



Stimulate successively at A and B with induction 

 shocks of moderate strength. A positive result will 

 be obtained in each case provided the nerve has not 

 TERMINING THE IR- been injured. Pour a small, quantity of 20 per cent. 

 HC1 upon the marble. Repeat the stimulations as 



NERVE. (Harvard soon as ^he COz has begun to pass over into the 

 chamber. It will be found that the stimulation at 

 A is now less effective than before or abolished altogether. Disconnect 

 the generator and blow fresh air into the chamber. Stimulate again. 

 Both excitations now give positive results. 



Annotation. The carbon dioxid destroys first the irritability and later on also 

 the conductivity. As this gas enters the chamber containing the nerve it diminishes 

 the irritability of the latter (A), but permits its conductivity to remain practically 

 normal (B) . Consequently, these properties of nerve are independent of one another. 



Pour a few drops of alcohol through the inlet tube of the gas chamber, 

 but in such a way that it does not come in contact with the nerve. 

 Stimulate at A as well as at B. It is to be noted that the stimulation 

 at B now remains ineffective, because the vapors of alcohol have de- 

 stroyed the conductile power of the nerve-fibers, while they have 

 diminished their irritability in a much slighter degree. 



3. Extensibility of Muscle. Use the same preparation; cut off the 

 nerve near the muscle, and fasten the femur in the clamp. Attach the 

 tendo achillis to the writing lever and adjust a large scale pan under- 

 neath the tendon. Release the after-loading appliance so that the 



