47 



and the sequence of events in the different parts and record 

 your observations. Time and note the number of contractions 

 of the ventricle in one minute. 



Now take the tip of the ventricle in the forceps and lift 

 it up and observe a fold of pericardium, the fraenum, which 

 is attached to it behind. Tilt the hind part of the frog up 

 and carefully snip this through, and then turn the ventricle 

 freely forward and study the changes which occur in the 

 sinus venosus, and the relation of these changes to the 

 changes in the other parts of the heart. 



2. Is the heart's action automatic ? Excise the heart with 

 the sinus attached, and place it in a watch glass and study its 

 movements, counting the number of beats per minute. 



3. Influence of Temperature. Now place the watch glass 

 upon ice and observe the effect. When a marked change in 

 the rate has taken place and been recorded, remove the 

 watch glass from the ice and place it upon the palm of the 

 hand and record any change in the rate. 



Method of Recording the Cardiac Cycle and of Studying the 

 Nervous Control of the Heart. 



1. Connect up the apparatus for giving a series of induced 

 shocks (Neef's hammer), inserting a commutator without 

 crossed wires into the secondary circuit with two pairs of 

 electrodes attached. 



2. Set a recording drum on the slow gear, and connect to a 

 small driving spindle. 



3. Kill a frog and remove the brain in front of the tym- 

 panic rings by cutting the head across at that level. Then 

 cut the spinal column and cord across between the shoulder 

 blades and pith the lower part, thus leaving the medulla 

 oblongata isolated and intact with the vagi passing from it 

 to the heart. 



| 

 A. To RECORD THE CARDIAC CYCLE. 



Place the cork plate with the frog directly under the heart 

 lever. Pin the frog firmly on the board by two pins close 

 to the heart, but not through the vagus nerve, and attach the 



