LESSON XT. 



GENERAL PROPERTIES OF NERVOUS TISSUE. 

 AUTOMATIC ACTIONS. 



A. REFLEX ACTION. 



1. Place on its belly a frog, which has been pre- 

 viously deprived of its brain 1 by the demonstrator. 

 Observe that its hind-limbs are drawn up under 

 the body; but that it differs from the normal 

 frog in the following respects. 



a. Its head is depressed, instead of being erect. 



b. Its fore-limbs are spread out, or flexed, instead 

 of being held nearly vertical ; thus the angle 

 which the body makes with the table is 

 diminished. 



1 This is done by cutting across the spinal cord just below the 

 skull and thoroughly destroying the brain with a seeker ; in order to 

 ensure the complete removal of the medulla oblongata, it is advisable 

 to destroy the parts a short distance down the 'spinal canal. The 

 frog should be left in a moist place for a day. Instead of this the 

 frog may be chloroformed the skull cut open and the brain re- 

 moved ; or the upper jaw with the anterior part of the skull may be 

 cut off with strong scissors and the medulla removed with forceps, 

 with this method the reflex action is often weak owing to the 

 considerable loss of blood. 



