Some of the more striking effects of de-afferentation in the spinal dogfish are diagrammatically represented in Fig. 13.

1. The persistent locomotory rhythm of a spinal dogfish depends upon afferent excitation. If all afferent excitation is cut off by severance of all dorsal roots, the rhythm is abolished (Fig. 13, 1).

2. The rhythm clearly emerges when about half the number of all the dorsal roots is transected, irrespective whether the anterior or the posterior half of the animal be de-afferentated (Fig. 13, 2 and 3), or whether complete unilateral de-afferentation is executed (Fig. 13, 4).

3. Extensively de-afferentated preparations may exhibit swimming movements after exteroceptive stimulation. These swimming movements do not persist.

4. Preparations de-afferentated except for the tail exhibit after exteroceptive stimulation a static reflex posture.

5. The de-afferentated musculature takes part in both tonic and rhythmic responses as long as it is connected through the spinal cord with normally innervated musculature.

6. In response to electrical stimulation applied to the cord of a spinal dogfish two distinct types of rhythmic response have been evoked.

7. No rhythmic responses have bee obtained through electrical stimulation of the spinal cord in completely de-afferentated preparations.

8. No evidence has been found in support of the view that the swimming rhythm emanates through a spontaneous, automatic activity from the central nervous system.

This content is only available via PDF.