252 Mr. J. S. R. Russell, On the Nerve Hoots of 



section, in order to allow of their being directly observed in action 

 when a nerve root was excited, the spinal cord was always first 

 divided transversely in the mid-dorsal region, so as to preclude 

 all possibility of the animal's being conscious of any pain, a possi- 

 bility most remote, seeing that it was always kept profoundly under 

 the influence of the anaesthetic in this as in all other experiments on 

 the nerve roots. 



When intravenous injections of absinthe were given, a jugular or 

 femoral vein was exposed, and a certain quantity of the essential oil 

 injected into the vein selected, by means of a hypodermic syringe. 



b. Excitation. The distal portion of the divided motor root was 

 separated from its sensory fellow, raised in the air by means of a 

 ligature passed round it, and stimulated by means of fine platinum 

 electrodes attached to the secondary coil of a du Bois Reymond's 

 inductorium supplied by a bichromate cell. Exactly the same appa- 

 ratus was used in excitation of the cortex cerebri (vide infra). 



DIVISION OF SUBJECT AND ANALYSIS OF RESULTS. 

 a. Division of the Subject. 



As in the previous research, I approached the question by simple 

 excitation of the peripheral end of the cut root, and observation of 

 the compound movement thus produced forms the first part of the 

 investigation. The next step was to carry out, if possible, a more 

 minute analysis of this combined movement, dividing it into its 

 component factors, e.g., by using minimal currents of excitation, 

 applied to the separate bundles of nerve fibres contained in the 

 nerve root. The strength of current necessary to produce the 

 maximum effect without diffusing to other nerve roots was found on 

 the average to be 500 to 600 on Kronecker's inductorium scale. 

 When minimum strengths of current were used for exciting the 

 separate bundles of nerve fibres of which a nerve root is composed, 

 the secondary coil stood at 40 to 50 on Kronecker's inductorium 

 scale, on an average. But both these readings naturally varied con- 

 siderably, according as the solution in the battery was fresh or old. 



The way in which I was led to suppose that each separate natural 

 bundle of nerve fibres of which a nerve root is composed might repre- 

 sent some simple movement, and that it might be possible to evoke 

 such a simple movement by exciting these separate bundles of nerve 

 fibres by minimal strengths of current, has been fully detailed in my 

 former paper. This minute differentiation is not so easily carried 

 out in the lumbo-sacral roots as was found possible in the cervico- 

 dorsal roots of the dog, owing to the fact that the distance between 

 the points of exit of the various nerve roots and those where they 



