A further important condition of the particular function with which we are now concerned (sensori-motor reflex) is that, from the present investigation, it seems certain that the path along which the impulses pass as evidenced by movement elicited in stimulating a certain posterior root, is directed towards a point below the level of that posterior root, and, not as we might suppose, chiefly in the same segment, or even above the level at which the posterior root joins the cord.
The proof of this new conclusion is afforded by many facts given in the paper, not the least interesting of which is, that on direct stimulation of the second or third anterior lumbar roots in the dog, no movement results in the lower limb, yet stimulation of the third posterior lumbar root gives distinct flexion and adduction of the hip and flexion of the knee, and stimulation of the second posterior lumbar root gives slight flexion of the hip and knee. In this connexion also results obtained by Claude Bernard, Schiiltze, Ramon-yCajal, Kolliker, Retzius, and Grolgi afford similar evidence.
Influence of the Posterior Roots upon the Nerve Centres in the Spinal Cord.
It was found that repeated excitation of the posterior roots decidedly increased the excitability of the posterior roots themselves, of the spinal cord and of the anterior roots. The difference in the excitability of the preparation before and after the previous stimulation may be represented by the fact that, whereas the minimal stimulus before the application of the repeated stimulus was represented by a distance of 50 cm. of the secondary from the primary coil in the condition of heightened excitability, a minimal stimulus was obtained at a distance of 70 cm. On the other hand, by cooling the posterior roots as suggested by Professor Gad, a converse effect was produced. The results of Belmonda and Oddi are also quoted in this connexion.
Results of Experiments upon the Spinal Cord in the Monkey.
Method.—The same as above.
The same general results were obtained by stimulation of the spinal cord in the monkey as described in the case of the dog. The area found excitable was the postero-external column, stimulation of which from the thirteenth dorsal segment to the second sacral segment inclusive produced after a very short latent period lateral flexion of the spinal column, flexion and adduction of the hip, flexion of the knee, ankle, and toes, movement of the tail and perinceum, and peristalsis (rumbling of the bowels), though it depended on the position of the electrode and the strength
