476 J. B. JOHNSTON 



izod l)y inoiius of cliloroforin phiccd on cotton in the mouth or 

 injected directly into the trachea or both. Although the resist- 

 ance of these animals was well known, in several cases the 

 anaesthesia was not carried far enough and the reactions to 

 cortical stimulation were prolonged contractions of neck muscles 

 or struggling movements of the limbs indicative of pain. In 

 these cases occasional responses, as of the eye muscles or temporal 

 muscle, appeared to be due to local excitation of the cortex but 

 the more extensive and prolonged movements were elicited from 

 any part of the cortex and were not distinguishable from the 

 responses to stimulation of the dura mater, the lower brain 

 regions or even the tissues exposed in the head. Under con- 

 ditions of deep anaesthesia the responses consisted of contraction 

 of a small set of muscles, and of short duration, and these were 

 obtained from a certain region of the pallium only. The lizards 

 are not so difficult to anaesthetize, but long continued appli- 

 cation of chloroform is necessary (one and a half to two hours 

 in a closed dish containing a wad of cotton wet in chloroform). 

 Another factor presenting difficulty is the small size of the 

 brain in these animals. This makes it necessary to use a single 

 point electrode or to have the two points very close together. 

 It is of the greatest importance that the meninges be carefully 

 removed from the whole hemisphere and that the brain and 

 surrounding tissues be kept as dry as possible without injury 

 to the brain tissue. If the electrode comes too close to the dura 

 mater or if fluid facilitates the spread of the current to the dura, 

 the muscles, thalamus or midbrain, the results are vitiated 

 because of responses coming from two or more sources of stimu- 

 lation. The responses which follow stimulation of the dura or 

 brain stem are very different from those produced by cortical 

 excitation, being usually more vigorous and prolonged as well 

 as more extensive. In the lizards and in several turtles, after 

 the dura was laid back and the olfactory and optic connections 

 were cut, the entire forebrain was raised out of the skull so as 

 to be free from contact with other tissues. Under these con- 

 ditions the entire surface of the hemisphere was explored with 

 the electrodes. 



