Object:
To record frog’s heart beat in situ
Image Source : media.merchantcircle.com
Requirements:
Sherrington’s revolving drum, Sherrington’s gaskell, heart lever, stand thread, small bent pin, board with cork sheet and living frog.
Procedure:
First we pith the medulla oblongata connected with the spinal cord (rotating a needle at this point), then expose and clear the heart but the heart is to be kept in situ.
ADVERTISEMENTS:
By destroying the nervous system there will be no effect of nervous system on heart and beat will be autonomic.
Add drop by drop 0 6% NaCl solution, then on the muscle at the tip of the ventricle a hook made up of from a small pin is passed through the apex without injuring the ventricular cavity.
The heart is gently lifted by a thread attached to the hook. The free end of the thread is tied to the heart lever with the help of the screw.
ADVERTISEMENTS:
The pointer of the lever is adjusted in a horizontal manner and pointer on the long arm of the lever is adjusted just to touch the smooth surface of the drum in order to reduce the friction of different speeds of the drum. The normal cardiographic records are registered on the smooth surface.
Observations:
The graphical records will show the following contractions:
(a) Auricular contraction:
Denoted by downward facing on the smooth drum.
ADVERTISEMENTS:
(b) Auriculo-ventricular pause:
In the form of a small straight or slightly inclined line.
(c) Ventricular contraction:
Just like an auricular contraction but the amplitude and height of contraction downward record is much longer than that of the auricular contraction.
Interpretation:
The contraction due to sinus venosus is not at all observed only because firstly sinus contraction is very weak and secondly auricular contraction is much more stronger as compared to sinus contraction.
Inference:
Under normal conditions the contraction of sinus venosus is generally followed by auricular contraction and ventricular contraction.
The downward tracing is the contraction and upward tracing is the relaxation of the heart, while small short tracings are the pause taken up by heart during series of each changes in each cardiac cycle.
Precautions:
The following precautions are to be taken:
1. Rotations of kymograph should not be fast otherwise contractions of the auricles will not be recorded.
2. The paper should be blackened well.
3. Edge of the pointer should be accurate.
4. Current flow should be uniform.
5. Heart should be kept wet in 0-6% saline solution.