52 



PRACTICAL PHYSIOLOGY 



the way described on p. 42, E, and a time tracing in - r -^th seconds 

 is recorded under the trace as described on p. 42, F. 



The effect of varying the 

 strength of the stimulus may be 

 investigated as on p. 46. 



The influence of load may be 

 studied by placing a rubber 

 band round the recording arm 

 of the lever and the end of the 

 frog-board and increasing the 

 load by moving the band out- 

 wards on the lever (p. 43). 



The influence of successive 

 stimuli and the genesis of 

 tetanus may also be studied 

 (p. 48, Lesson XI. 2). 



J. THE CONTRACTION OF 

 CARDIAC AND OF VIS- 

 CERAL MUSCLE 



1. Character of a Single Ven- 

 tricular Contraction (Cardiac 

 Muscle). 



Use the body of the frog 

 from which you made your 

 muscle nerve preparation. Ex- 

 pose the heart as described in 

 Lesson XIV. p. 61, and separate 

 the sinus from the auricles by 

 applying the first Stannius 

 ligature (p. 64). 



After the ventricle has been 

 stopped take a trace on a 

 moderately fast drum (fast-gear 

 small spindle to the largest on 

 the drum] of the contraction 

 caused by touching the ven- 

 tricle. The touch will record 

 the moment of stimulation on 

 the drum. Take a time trace 

 in yoth sec. and measure the 

 1 duration of the phases. 



2. Character of the Contractions 

 of Muscle of Frog's Stomach 

 (Visceral Muscle). 



Kill a frog and open the abdomen. Identify the stomach and 

 cut with sharp scissors a ring about two or three millimetres wide 



