PRACTICAL EXERCISES 



961 



decapitation. The large electrode is placed on a shaved part of a fore- 

 arm. Various effects may be elicited according to the point of the cross- 

 section stimulated e.g., stepping and scratch movements of the hind- 

 limbs. Other facts mentioned in the text in regard to spinal reflexes can 

 be verified on this preparation. 



9. Reflexes in Man. Study systematically on a fellow-student and 

 on yourself the chief reflexes described in the text (p. 886), especially 



The Knee-jerk. (i) Elicit the jerk in the usual way by striking the 

 ligamentum patellae and observe its height. Then cause the patient to 

 make a strong voluntary movement (squeezing the hands together or 

 clenching the jaws) at the moment when the 

 tendon is struck, and note whether the height is 

 increased by ' reinforcement.' 



(2) Attach a suitable recording apparatus to 

 the foot of a person sitting with his legs over the 

 edge of a table, and record the jerks elicited by 

 taps made as uniform in strength as possible. A 

 small hammer worked by an electro-magnet or a 

 spring might be employed for this purpose. Com- 

 pare the records obtained when the jerk is elicited 

 while the person is squeezing his hands together 

 with those previously obtained. The influence of 

 mental activity, especially of excitement or irri- 

 tation (opportunities of studying such psychical 

 states occasionally offer themselves in physio- 

 logical laboratories) in increasing the height of 

 the knee-jerk may also be verified (Lombard). 



10. Excision of Cerebral Hemispheres in the 

 Frog (Fig. 383). Anaesthetize a frog lightly by 

 puttingit under a bell-jar or tumbler with a small 

 piece of cotton-wool soaked in ether. Put very 

 little ether on the cotton, and leave the frog only 

 a very short time under the bell- jar. Then, 

 holding it in a cloth, make an incision through 

 the skin over the skull in the mesial line. With 

 scissors open the cranium about the position of a 

 line drawn at a tangent to the posterior borders 

 of the two tympanic membranes. Remove the 

 roof of the skull in front of this line with forceps, 

 scoop out the cerebral hemispheres, and sew up 

 the wound. As soon as the animal has recovered 

 from the ether, the phenomena described at 

 p. 915 should be verified. The frog will swim 

 when thrown into water, will refuse to lie on its 

 back, and will not fall if the board on which it lies be gradually slanted. 

 Let the frog live for a day, keeping it in a moist atmosphere; then 

 expose the brain again, determine the reflex time by Tiirck's method ; 

 apply a crystal of common salt to the optic lobes, and repeat theobserva- 

 tion. The reflex movements will be completely inhibited or delayed. 

 Remove the salt, wa?h with physiological salt solution, excise the optic 

 lobes, and see whether the frog will now swim. 



1 1 . Excision of the Cerebral Hemispheres in a Pigeon. Feed a pigeon 

 for two or three days on dry food, etherize it by holding a piece d 

 cotton-wool sprinkled with ether over its beak, or inject into the rectum 

 | gramme chloral hydrate. The pigeon being wrapped up in a cloth, 

 and the head held steady by an assistant, the feathers are clipped off the 



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Fig. 383. Brain of Frog 

 (afterSteiner). a, cere- 

 bral hemispheres; b, 

 position of optic thala- 

 mi; c, optic lobes; d, 

 cerebellum ; e, medulla 

 oblongata ; A , upper 

 end of spinal cord. 



