THE DECEREBRATE PREPARATION. 249 



a quick retraction of the pinna accompanied often by a folding 

 back of its free end. 



2. THE ACOUSTIC REFLEX. Pricking up of the ears when a sharp 

 sound is made as by clapping the hands. This reflex occurs 

 only when the section is forward of the anterior corpora quad- 

 rigemina. 



3. THE DEGLUTITION REFLEX. Swallowing movements when 

 water is dropped on the base of the tongue. Note the behaviour 

 of the respiratory movements during the swallows. Repeat the 

 observation by dropping the water on various parts of the tongue. 

 Observe the effect on swallowing produced by pressing a moist- 

 ened camel's hair brush on the pharynx. In order to do this, 

 it is necessary to slit the soft palate in the mid line. The move- 

 ments of the vocal cords can readily be observed by using a 

 laryngeal mirror. 



4. THE HEAD-SHAKE REFLEX. Rapid shaking movements in 

 rotary direction when air is blown into the external auditory 

 meatus. The reflex may also be elicited by squirting cold water 

 from a syringe into the ear. 



5. THE FLEXION REFLEX. By painful stimulation of the paw 

 flexion at knee and hip occurs. 



6. THE KNEE JERK. Quick extension (kick) at knee produced by 

 tapping the patellar tendon. Note particularly that the return 

 of the leg after the contraction is not complete, and that if the 

 tendon be tapped at short intervals the knee becomes more or 

 less permanently extended. This result depends on a contrac- 

 tion remainder, which is a feature of the 'rigid' postural muscles 

 in decerebrate preparations. In the spinal animal there is no 

 postural hypertonus so that, the leg passively falls back to its 

 previous position after the jerk. 



The scratch reflex is not present as a rule. 



The most striking reflex condition produced by the decere- 

 bration is the rigidity, which it can readily be seen affects parti- 

 cularly the extensor (postural) muscles. The rigidity is not of the 

 same nature as the tetanic contraction produced by continuous 

 stimulation of the motor neurone, for the muscle yields to a slowly 

 applied pull and does not spring back to its old position when the 

 extending force is removed. This is tested by bending the knee or 



