1). Remove (.-are fully the optic l<il>es. wash oft any exec-- -alt 

 with physiological salt -olntion. and again determine the reaction 

 tinu. Any change: X\v sew carefully together the tla]>- of -kin 

 over the brain cavity. C mpare it- reactions with tho>e of the 

 decerebrate frog of experiment jjS. Place the frog in the box 

 to be kipt t"r observation next day. 



///. BIOELECTRIC CURRENTS 



j^o. (. \i pillar \ elect r i nneter. The inertia of the coil of the 

 ordinary d'. \r-on\al gal\ anometcr is so great that it is nnsuited to 

 rec I'd rapid changes in potential such as are produced by actively 

 functioning plant and animal ti--ues. For this purpose the capil- 

 lary electrometer is used. The wire- are attached to two snrtace- of 

 mercury, one large and one small I in a capillary tube), -eparated 

 from each other by _>o' , -ulphuric acid. When a current passes, the 

 mercury in the capillary moves in the direction of the current. 

 M "\cimnt is proportional to the strength of the current and de- 

 pend- on a change in the surface tcn-i; n of the mercury. It- 

 -urface tension i- greatest when the potential difference across the 

 surface i- least. Draw a diagram -bowing the construction ot the 

 capillary electrometer. A detailed description of the instrument 

 will be found in I b >well, p. o,S. 



X te the >hort circuiting key on the instrument. Non-polarizable 

 electrode- nm-t alwa\ - be u-ed in leading oil the wires trom the 

 ti--ue to the galvanometer. 



Fill the tubes of the capillary electrometer with mercury and Jo', 

 sulphuric acid and -et up on the stage of a microscope a- demon- 

 strated. I landle the parts rrry carefully, as the in-trumcnt is expen- 

 sive and easily broken. Wax cement may be used to hold the tube- 

 firmly in the block support. The prc--urc tube on the right will 

 n t lie u-ed for these experiments. 



2$\. The action current of the heart. Non-polarizable electrode- 

 are applied to ventricle and auricle of the frog'- bear! while in th 

 body and connected to the capillary electrometer on the micro-cope. 

 Heart mu-cle. like every other muscle, becomes during contraction 

 electrically negative relatively to inactive portions ot the tissue. A 

 wave of contraction accompanied by a wave ''I negative potential 

 pa is o\er the heart and is recorded b\ the electrometer. I >o the 

 excursions of tin- mercury correspond to the heart heat-: 



j^j. "/'//( current of injury (current of rest or demarcation cur- 

 rent) of muscle. A -artorius muscle i- carefully prepared and one 



3 



