74 ELECTRO-PHYSIOLOGY CHAP. 



not hold in a strict sense within the central organ as in the 

 peripheral nerves, the same is true of another great law, viz. 

 that of " conductivity in both directions." The efferent (especi- 

 ally motor) and afferent nerves are known to enter the spinal 

 cord of vertebrates by different roots. Central excitation of a 

 divided anterior root never (even after strychnin poisoning) 

 discharges any reflex movement or spasm. With regard to the 

 structure of the cord we should, therefore, conclude that the 

 protoplasmic processes of the cells of the anterior horn, in so far 

 as they serve to transmit excitation, do so in one direction only. 

 It would thus be characteristic of these cells that they confined 

 the conductivity, which in ordinary nerve-fibres is in both direc- 

 tions, to one direction only (Gad). Recent conclusions as to the 

 constitution of the gray matter, and more particularly the ana- 

 tomical structure of the reflex arc, place the matter in another 

 aspect. For if instead of continuity of substance we have merely 

 contact between the end-branches of the conducting nerve-fibre 

 (" terminal arborisations ") and the " reflecting " (motor) cells of 

 the ganglion, conduction in one direction becomes intelligible, 

 and is no more surprising than the fact that excitation of a muscle 

 does not simultaneously excite its motor nerve. 



There is a striking dissimilarity in the action of strychnin 

 upon different animals, pointing to corresponding and quite un- 

 known differences in the chemical composition of the central 

 nerve-cells. Among vertebrates, guinea-pigs and fowls are char- 

 acterised by a special insensibility to strychnin (Leube, 32). 

 And in most invertebrates the characteristic spasms are wanting, 

 even with large doses of the poison. Claude Bernard first made 

 the (often-confirmed) observation that the reflex excitability of 

 invertebrates (crayfish, leech) is not altered by strychnin. Both in 

 leech and crayfish the stages of excitation characteristic of verte- 

 brates were entirely wanting, and he found only a rapid and primary 

 (central) paralysis. Krukenberg (33) confirmed Bernard's con- 

 clusions, while Yung (34), on the contrary, witnessed sharp 

 tetanic spasms in the crayfish which soon gave way to paralysis. 

 Luchsiuger (35), too, pointed out in invertebrates (leech, crayfish) 

 that had been poisoned with strychnin, phenomena which he 

 regarded as reflex spasms. In any case these only appear under 

 certain conditions. Luchsinger, like Krukenberg, employed the 

 ingenious method, first devised by C. Bernard for the frog, of 



