PRACTICAL EXERCISES 



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. 947 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 the 



observation. The reflex movements will be 



completely inhibited or delayed. Remove the 



salt, wash with physiological salt solution, 



excise the optic lobes, and see whether the 



frog will now swim. 



14. 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 of 



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 assis- 

 tant, the feathers are clipped off the head, an 



incision made in the middle line through the 



skin, and the flaps reflected so as to expose 



the skull. Cut through the bones with scissors, 

 and make a sufficiently large opening to bring the cerebral hemispheres 

 into view. They are now rapidly divided from the corpora bigemina 

 and lifted out with the handle of a scalpel. The bleeding is very free, but 

 may be partially controlled by stuffing the cavity with the vegetable 

 fibre known as Pengavar Djambi, which should be removed in a few 

 minutes, the wound cleansed with iodoform gauze wrung out of physio-, 

 logical salt solution at 50 C., and sewed up. Study the phenomena 

 described on p. 948. 



15. Stimulation of the Motor Areas in the Dog. (a) Study a hardened 

 brain of a dog, noting especially the crucial sulcus (Fig. 382, p. 950), the 

 convolutions in relation to it, and the areas mapped out around it by 

 Hitzig and Fritsch and others. (6) Inject morphine under the skin of 

 a dog. Set up an induction-coil arranged for tetanus, with a single 

 Daniell in the primary circuit. Connect a pair of fine but not sharp- 

 pointed electrodes through a short-circuiting key with the secondary. 

 Fasten the dog on the holder, belly down, and put a large pad under the 

 neck to support the head. Clip the hair over the scalp. Feel for the 

 condyles of the lower jaw, and join them by a string across the top of the 

 head. Connect the outer canthi of the eyes by another thread. The 

 crucial sulcus lies a little behind the mid-point between these two lines. 

 Now give the dog ether, make a mesial incision through the skin down 



Fig. 402. Brain of Frog 

 (after Steiner). a, cere- 

 bral hemispheres ; b, 

 position of optic thala- 

 mi; c, optic lobes; d, 

 cerebellum; e, medulla 

 oblongata ; A , upper 

 end of spinal cord. 



