557 



LABORATORY EXPERIMENTS ON MUSCLE AND NERVES. 



Physiological experiments on living muscle serve to demonstrate many 

 of the most fundamental particulars of physiology. The muscles of 

 cold-blooded animals isolated from the body retain their living attributes 

 for hours under laboratory conditions. They illustrate practically all the 

 facts shown by the muscles of warm-blooded animals. 



i. The Use of the Induction Coil. The induced current obtained by 

 means of an apparatus called an induction coil is the most convenient and 

 reliable means of stimulating the muscle or the nerve. The arrangement of 

 the batteries, keys, and coils for the ordinary muscle work is shown in figure 

 350. The strength of the induced current decreases with the distance of the 

 secondary coil from the primary, but according . to a logarithmic curve. 

 For ordinary work the centimeter scale is adequate guide for the proportionate 

 strength of the induction current. 



FIG. 350. Diagram illustrating the relations of the battery, keys, coils, and electrodes as 

 used for physiological stimulation. 



At the moment of closure of the primary key, a current of electricity is 

 induced in the secondary coil, the make current. The induced current is 

 only momentary in duration, i.e., does not continue though the primary circuit 

 is complete. Also when the primary current is broken by opening the key a 

 second current is induced, the break current. The former is in the opposite 

 direction to, the latter in the same direction as the primary current. In 

 ordinary coils the break current is stronger. The induction coil may be used 

 to produce a rapid series of shocks by means of a magnetic interrupter, as in 

 the Harvard inductorium. 



a. Test the strength of a series of single make induction shocks beginning 

 with the weakest possible position of the secondary coil, and going toward the 

 primary coil i cm. after each test. Test the stimulating effect by applying 

 the electrodes to the tip of the tongue. Record the results as directed by the 

 table below. 



