which give- the -timulu-. Take at least two records and determine 

 the average time required to react to a -limnlus. 



226. f\'ciiction time ;*.'ith choice. Apparatus as in the preceding 

 experiment except that three ke\ - are placed in the circuit and the 

 stimulating electrode- are luld mi the tongue by the lips. Right and 

 left hands are placed on two of the key> ( hoth closed) and if a 

 5tr ng -timulus is received the left hand opens a key; if a weak 

 stimuli!- the right hand. Strong and weak stimuli must he deter- 

 mined beforehand in terms of coil distances and of course the 

 ubject must not know which he is to receive. Take two nv inl- 

 and compare with the preceding experiment. 



i 227. AY//r.r tone of muscles. I'ith the brain Miily of a frog 

 and suspend from a hook hy the lower jaw. Xote especially the 

 position of the leg-, \o\\- make a small -lit in the abdomen and 

 cut the roots nl all the nerves going to the right leg where they 

 leave the -phial cord. Again -u-pend the frig fnun the honk and 

 note the position of the legs. \\ hat does thi- experiment indicate.' 



I!. Till'. IJkAi.v 



In the following operations proceed very -lowly and cautioti-ly. 

 as the frigs are to he kept alive for as long a time as pn--ihle t" 

 recover from "cerebral shock", due to the operation. I'se well 

 sharpened instruments. At intervals during the operation wash the 

 skin with antiseptic salt solution ( I IgVL I : JCOG). 



228. I\'emo:'al of hemispheres. Select a male hog. characterized 

 by a thickened pad on the innermost digit of the front limb. 

 Anacstheti/c by placing him under a battery jar with - me absorbent 

 cotton \\et with ether. If during the following operation the effect 

 of the anaesthetic diminishes, place under the jar again. 



The cerebral hemispheres of the trog extend back to a line con- 

 necting the front margins of the two tympanic membranes. ( ni the 

 skin along this line over the top . I the -kull. Lrom this cross cut 

 make a median incision forward nearly to the iio-tn]-. Lav back 

 the Hap-. With -cis-or point- separated to either side o| the top 

 of the skull, immediately in front of the transverse skin incision, 

 cautiously bring ihe points together, cutting hareh through the bone. 

 In-ert the -bar] blade forward and at one side under the bony 

 covering of the cerebrum, and snip the bone. Kcpeat the operation 

 on the other sjdi.'. l\ai-e the bone with -mall lorccps and carefully 

 cut forward, alternate!) on one sjdc and the Other, until the cere- 

 brum i- entirely eNpn-ed. Sever the Connections between the optic 



