Mammalian Nerve- Muscle and Rejlex Preparations. 351 



steadily during the flow of a strong descending current. The strength of 

 stimulation required to produce a continuous effect in this case is far greater 

 than that in the case of nerve-muscle preparations. The inhibitory reflex 

 effect at break of a powerful ascending current is often prolonged. The 

 rebound contraction following it, is limited, as it is depressed by prolongation 

 of the inhibitory process. 



The above experimental data show that there is a continuous reflex effect 

 during the passage of a strong descending polarising current through the 

 afferent nerve in the extensor reflex preparation, which is not present if the 

 current is reversed in direction. The results in this preparation of stimula- 

 tion by constant galvanic currents show full agreement with those in the 

 flexor reflex and nerve-muscle preparations. In order to produce a con- 

 tinuous effect from the afiereut nerve, the current required is, however, far 

 stronger than that for the nerve-muscle preparation. 

 . These reflex results in the extensor reflex preparation bear some resem- 

 blance to the changes in the respiratory movement observed by Langendorff 

 and Oldag (5), as a result of the application of constant galvanic currents 

 to the central stump of the cut vagus. 



In some preparations in which walking movements occurred without any 

 artificial stimulation, these movements were inhibited whenever a weak 

 polarising current was led into the nerve in descending direction. On the 

 contrary, ascending currents either augmented the movements or produced no 

 effect upon them. Sometimes, in the latter case, the walking movements, 

 which were not present before stimulation, were superadded to the usual 

 reflex results (fig. 3). 



(4) The Response hy Excitation m' Inhibition modified hy Factors other than 

 those involved in Stimulation. 



The complexity and multiplicity of reflex results in the extensor reflex 

 preparations are dependent on other factors than those already mentioned as 

 influencing the functional condition of the central nervous mechanism. In 

 the presentation of the results of these experiments, as detailed above, the 

 more typical have been selected. There were, however, cases in which the 

 responses were altered, by variation in the degree of decerebrate rigidity, in 

 the initial length of the tonic muscle, and in the position of the neck and 

 other joints : — 



(i) The intensity of decerebrate rigidity developed in the preparation varies 

 in different cats and is influenced by the depth of anaesthesia and the time 

 which elapses after decerebration. In some preparations, especially those 

 with poor rigidity, excitatory reflex effects are entirely, or almost entirely, 



