54 EXPERIMENTAL GENERAL PHYSIOLOGY 



The increase of the strength of stimulus beyond the optimum will 

 only fatigue the muscle and nerve through overstimulation, without 

 producing greater contractions. 



4. Observations. (1) Take tracings of the contractions produced 

 by a series of "make-induction shocks" applied indirectly i. e., 

 to the nerve. The "make-induction shock" is obtained as 

 follows : 



(a) With primary circuit not interrupted by the Neef hammer, but 

 closed and opened by the contact key, open the short-circuiting key 

 of the induced circuit. 



(6) Close the contact key of the primary circuit and make induc- 

 tion shock i. e., a shock in the induced circuit caused by a closure 

 of the battery circuit will stimulate the preparation. 



(c) Close the short-circuiting key in the secondary circuit. 



(d) Open or break the primary circuit. An induced break shock 

 occurs in the secondary circuit, but it is short-circuited by the closed 

 Du Bois-Reymond key. If while the drum rotates one makes, in 

 close succession, the changes above indicated a-b-c-d, a-b-c-d, etc. 

 there will be produced a series of contractions, all the result of 

 stimulation by make-induction shocks. 



(2) Take a tracing of the contractions resulting from a series 

 indirectly applied break-induction shocks. 



(3) By leaving the short-circuiting key open one may get a series 

 of contractions due to alternating make-induction shocks and 'break- 

 induction shocks. Let these be recorded in pairs upon the kymo- 

 graph. 



XII. THE TYPICAL MYOGRAM, COMBINED MYOGRAMS, 

 AND TETANUS. 



1. Appliances. Inductorium; Daniell cell or dry cell; kymograph; 

 myograph; electrodes; keys; wires. 



2. Preparation. Pith a frog, make muscle-nerve preparation; 

 mount it on myograph, prepare kymograph for tracing, and adjust 

 for fastest rotation; set up electric apparatus for a series of make- 

 induction shocks or break-induction shocks. 



3. Experiments and Observations. (1) Start the kymograph 

 drum to rotating. When it has reached the maximum speed, stimu- 

 late the preparation with a break-induction shock. The lever point 

 should trace upon the drum a typical myogram. Repeat the experi- 

 ment several times with the same preparation. Study the character- 

 istics of the myogram. 



(2) Trace another myogram while a tuning fork is tracing hun- 

 dredths of seconds upon the drum and while the instant of stimulating 

 the nerve is traced upon the drum, either through the action of an 



