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Dr. C. S. Sherrington. 



slitting and turning aside of the dura mater. The cortex has then 

 been stimulated by rapidly repeated induction shocks, obtained by 

 the Da Bois inductorium. The Helmholtz equaliser has always 

 been employed. The intensity of the faradic currents used has 

 been usually such as to be barely perceptible when the platinum 

 electrodes were applied to the tongue-tip. The anaesthetics used 

 have been either ether alone or ether mixed with chloroform in 

 equal volumes. The degree of narcotisation forms an important 

 condition for the prosecution of the observations. When the narcosis 

 is too profound the results to be recorded are much less obvious than 

 when the narcosis is less deep. It is best, starting with the animal 

 in a condition of deep etherisation, to allow that condition gradually 

 to dimmish. A_s this is done it almost constantly happens that at a 

 certain stage of anaesthesia the limbs instead of hanging slack and 

 flaccid assume and maintain a position of flexion at certain joints, 

 notably at elbow and hip. This condition of tonic contraction having 

 been assumed, the narcosis is, as far as possible, kept at that par- 

 ticular grade of intensity. The area of cortex cerebri previously 

 ascertained to produce under faradisation extension of the elbow- 

 joint or hip-joint is then excited. 



For clearness of description we will suppose that the left hemi- 

 sphere is excited, and that, therefore, the limb affected is the right. 

 The result of excitation of the appropriate focus in the cortex, e.g., 

 that presiding over extension of the elbow, is an immediate relaxation 

 of the biceps, with active contraction of the triceps. As regards the 

 condition of the biceps, the relaxation is usually so striking that 

 merely to place the finger on it is enough to convince the observer 

 that the muscle relaxes. The following is, however, a good mode of 

 studying the phenomenon : In a monkey with strongly developed 

 musculature the forearm, maintained by the above-mentioned steady 

 tonic flexion at an angle of somewhat less than 90° with the upper 

 arm, is lightly supported by the one hand of the observer, while with 

 the finger and thumb of the other the belly of the contracted biceps 

 is felt through the thin skin of the upper arm. On exciting the 

 cortex the contracted mass becomes suddenly soft — as it were melting 

 under the observer's touch. At the same time the observer's hand 

 supporting the animal's forearm tends to be pushed down with a 

 force unmistakably greater than that which the mere weight of the 

 limb would exert. If the triceps itself be felt at this time it is easy 

 to perceive that it enters contraction, becoming increasingly hard 

 and tense, even when its points of attachment are allowed to 

 approximate, and the passive tensile strain in it should diminish. If 

 the limb be left unsupported the movement is one of simple extension 

 at the elbow-joint. On discontinuing the excitation of the cortex the 

 forearm usually immediately, or almost immediately, returns to its 



