426 MESSRS. F. GOTCH AND V. HORSLEY 



main supply of each nerve is, in the case of the Cat, one root lower than in that of the 

 Monkey. 



The physiological connections of the roots were of importance to us only as far as 

 the fibres in the sciatic nerve were concerned. In attempting to ascertain these con 

 nections it occurred to us that the electrical method would furnish a valuable means 

 of ascertaining to what extent the fibres in any nerve trunk are derived from particular 

 roots, whether anterior or posterior. All that is necessary for the carrying out of such 

 investigation upon the sciatic nerve is to expose the oauda equina of an anaesthetised 

 animal, then to prepare the nerve, divide it, and connect its isolated central end with 

 the galvanometer. The various roots of the lower lumbar nerves are now divided at 

 their termination in the spinal cord, and their peripheral ends excited with the inter 

 rupted induction current for a given time (5 seconds). If electrical effects are evoked 

 in the central end of the divided sciatic, then, obviously, the root excited contains 

 nerve fibres which pass down the nerve as far as the region observed. With the 

 animal in a state of uniform narcosis, the comparative amounts of the deflection pro 

 duced by applying to the different roots a stimulus of unvarying intensity and duration 

 indicate the relative amount of fibres, provided that the excitability of the various 

 roots is approximately the same. In this way we ascertained that the effect evoked 

 in the popliteal region by exciting the peripheral ends of the cut anterior or posterior 

 roots of the 1st sacra] nerve was, in the Cat, comparatively small, being only one- 

 sixth of that evoked by exciting those of the 7th or 6th lumbar, whilst excitation of 

 the 5th and 4th lumbar was followed in the Cat by very little effect at all in the 

 nerve. Physiological experiment thus bears out the anatomical details displayed by 

 dissection. One obvious use of the method which the few experiments which we have 

 carried out on this line suggests is, that it not only secures an analysis of the different 

 fibres which pass from a complicated plexus into a nerve, but places within the expe 

 rimenter s grasp a method of determining to what extent the relations of the afferent 

 fibres of a nerve with the nerve roots are similar to those of the efferent fibres. 



We will now turn to our experimental results made upon the cord itself. 



SECTION 5. THE OPERATIVE PROCEDURE INVOLVED IN THE METHOD OF SECTIONS 



INTERVENING BETWEEN THE OBSERVED CoRD AND THE EXCITED NERVES. 



The experiments were made upon twenty-two Cats and three Monkeys, and were 

 all conducted in the following way. The cord of the anaesthetised animal was 

 exposed and divided in the lower dorsal region, the particular locality varying from 

 the levels of the 8th to that of the llth dorsal vertebras. It was then prepared for 

 4 centims. on the distal side of the section and connected at its cut and longitudinal 

 surface with the non-polarisable electrodes by cables, in the same manner as that 

 already described. (See Chapter HI., Section 3.) The sciatic nerve was then 

 exposed, freed for some distance, ligatured, and divided. It was left in the muscles 



