418 ON SOME FUNCTIONS OF THE ENCEPHALON. 



which arc called forth by external stimuli, rendering them very 

 complicated and delicate, especially giving them features which 

 cause them closely to resemble ordinary voluntary movements, 

 and suggesting the idea of intricate arrangements within certain 

 parts of the brain, of afferent (including nerves from the sense 

 organs) and efferent nerves and nervous centres, which may be 

 set into action by volition on the one hand, or by some external 

 stimulus on the other. 



06s. IV. Inhibitory Influence of parts of the Brain over the 

 Reflex Actions of the Spinal Cord. 



The reflex actions of the cord much more readily occur, and 

 are much more vigorous and complete, in the absence than in 

 the presence of the brain. The brain, therefore, must in some 

 way or other prevent reflex actions. 



Irritation <>f tit*' <ij>tir lobes Having prepared a frog, as in 

 o/,s. II. etc., ascertain the intensity of the reflex activity by the 

 sulphuric acid method. (Chapter XXXIII., Obs. VI.). 



Touch with a small crystal of sodium of chloride, or with the 

 point of a brush dipped in saline solution, the cut surface of 

 the optic lobes and determine, after a few seconds before con- 

 vulsions, which may occur, have set in, the duration of the 

 interval between the exposure of the foot to the acid and its 

 withdrawal. It will be found to be greatly prolonged. In 

 other words, irritation of the optic lobes has interfered with, or 

 partially inhibited, the reflex action of the cord. If the optic 

 lobes be removed, and the medulla irritated instead, the result 

 will be much less marked. 



n/;s. V. Having prepared a frog with optic lobes, and deter- 

 mined the reflex interval as above, inject into the back grain 

 of quinine sulphate, and determine the interval again from time 

 to time. It will be found to be much prolonged. 



Having prepared a frog with divided medulla (Chapter 

 XXXIII.), and determined the duration of the reflex interval, 

 inject the same quantity of quinine, and again determine the 

 interval as before. No prolongation of the interval will be ob- 

 served. These results may be explained by supposing that the 

 quinine is unable to act directly on the reflex activity of the 

 cord, but is able either to stimulate an inhibitory mechanism 

 in the brain, or at least to affect the brain in such a manner as 

 to interfere with the reflex actions of the cord. 



O//s. V 1. Jtriiini'fil of the Crrelirnl Jti'in /*j>/irrt>* in the Bird. 

 SeK-ct a vigorous pigeon, so young as to be just able to fly well. 

 Keep it on dry food for a few days, in order to avoid an excess 

 of bleeding. 



Having placed it under chloroform, using as little chloro- 

 form as possible, make an incision in the median line over the 

 roof of the skull, and hook back the two flaps of skin. The 

 thin skull may now be easily cut through with a pair of scis- 



