Book Description

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1906 edition. Excerpt: ...use of electric stimuli some polarization may be added. Yet its local character does not at all necessarily imply its reference to the skin. It may be the expression of a spatial arrangement in the central organ by which reflex-arcs arising in adjacent receptors are partially confluent in their approach toward the final common path, and are the more confluent the closer together lie their points of origin in the receptive field. The resemblance between the distribution of the incidence of this fatigue and that of the spatial summation previously described argues that the seat of the fatigue is intraspinal and central more than peripheral and cutaneous; and that it affects the afferent part of the arc inside the spinal cord, probably at the first synapse. Thus, its incidence at the synapse Ra--Pa and at R/3--P/9 (Fig. 13, B, or 39, B) would explain its restrictions, as far as we know them, in the scratch-reflex. The local fatigue of a spinal reflex seems to be recovered from with remarkable speed, to judge by observations on the reflexes of the limbs of the spinal dog. A few seconds' remission of the stimulus suffices for marked though incomplete restoration of the reaction (Fig. 63). In a few instances I have seen return of a reflex even during the stimulation under which the waning and disappearance of the reflex occurred. The exciting stimulus has usually in such cases been of rather weak intensity. In my experience, these spinal reflexes fade out sooner under a weak stimulus than under a strong one. This seeming paradox indicates that under even feeble intensities of stimulation the threshold of the reaction gradually rises, and that it rises above the threshold value of the weaker stimulus before it reaches that of a stronger...