Effects of Experimental Block of the Amphibian Nervous System.

Abstract

Experiments previously reported 1 have shown that the cut ends of the spinal cord can be prevented from reuniting by the removal of a comparatively large amount of the nervous system and the implantation into the wound of the anlage of the limb and pronephros.

The responses of such an embryo during early stages are strictly in keeping with the findings of Coghill and Harrick. The uninjured portions of the nervous system behave as individual units and take up their function with a very slight delay over the normal. As the animals differentiate, a complex series of reactions occurs by means of which stimuli are transmitted across the gap in the nervous mechanism. This transfer of stimuli takes place through the intermediation of the musculature which is in that region.

The first integration of response was noticed in the reactions occurring after stimulation in the head region. The sensory pick-up is mediated through the uninjured medulla giving rise to a motor response through the 7th cranial nerve which activates the gular musculature and the arcuate muscles of the gills. This reaction is transmitted to the anterior trunk region where the sensory pick-up acts in the pectoral region to transmit the stimulus to the uninjured cord of the trunk. This motivates the musculature of the flank and tail and gives rise to distinct swimming movements.

The limbs which have been transplanted into the wound area develop synchronously with the normal limbs. They are generally single and although they develop in close proximity to the gills, show no trace of the developmental dominance of that tissue. In every case the laterality of these limbs has been that of the side from which they were taken.