26 EXPERIMENTAL PHYSIOLOGY. 



be studied by obtaining a record of the muscle on a rapidly 

 moving drum. A gastrocnemius preparation in the moist 

 chamber is prepared for direct stimulation by connecting each 

 end of the muscle to a binding post (Fig. 5). These binding 

 posts are connected in turn to the terminals of the secondary 

 coil. Moist filter paper in the chamber will prevent drying of 

 the muscle. 



The muscle lever must be in such a position that it will 

 continue to write on the drum when the muscle contracts. 

 Weight the scale pan sufficiently to permit an appropriate 

 excursion of the lever. Adjust the after-loading screw so that 

 the resting muscle does not support this weight. The electro- 

 magnetic signal should be supported on the same stand as the 

 muscle lever and its writing point should be close to the writing 

 point of the muscle lever, in line vertically with it. Always 

 make alignment marks on the drum with all writing points 

 before recording a muscle contraction. Both the electromag- 

 netic signal and the kymograph should be introduced into the 

 primary circuit of the inductorium. 



After determining a suitable strength for the stimulating 

 current, record a contraction, using the spring-driven drum. 

 By means of the lever at rest, record below this a base line. 

 Now draw an arc with the lever from the point of maximal 

 contraction to the base line. Obtain a tuning fork record 

 between the base line and signal line. 



In this manner secure three or more good records. After 

 the paper has been removed from the drum and the surface 

 fixed with rosin, determine the time for the latent period, 

 contraction period and relaxation period. 



If you have time obtain additional records in which the 

 after-loading screw is changed, so that the load is picked up 

 earlier or later than at first. 



Discuss the factors which might be involved in production 

 of the latent period. 



Experiment 8a. Modification for Harvard Kymograph. The 

 writing point of the signal magnet must be in a vertical line 

 with the writing point of the muscle lever. Signal magnet and 

 muscle lever are clamped as close together as possible on the 



