The objective of this study was to examine anatomically the distribution of afferent neurones in the mesencephalic nucleus of the fifth nerve (Mes V). HRP was applied, in separate experiments, to the inferior alveolar, infraorbital, and masseter nerves, and injected into the masseter muscle and periodontal ligament. Following application of HRP to the masseter muscle and masseter nerve, labelled cells were found in the ipsilateral motor nucleus of the fifth nerve and in the ipsilateral Mes V. Labelled cells in Mes V, identified as belonging to proprioceptor afferents from jaw-closing muscles, were distributed throughout the full extent of the nucleus. Following application of HRP to the inferior alveolar nerve, infraorbital nerve, and periodontal ligament, labelled cells were found in the ipsilateral trigeminal ganglion and Mes V, and the latter identified as belonging to periodontal receptor afferents. In contrast to the distribution of spindle afferent somata, they were restricted to the caudal region of Mes V. The differential distribution of afferent neurones within Mes V demonstrated in this study confirms previous electrophysiological findings, and its significance is considered.

SUMMARY1. Continuous elevation of the middle finger for 15-60 min gave rise to modulation of the e.m.g. at 4-6 Hz. A marked peak (50-150 % of the amplitude of the coexisting 8-12 Hz peak) at 4-6 Hz was produced in sixteen out of twenty-one subjects.2. The 8-12 Hz peak was also enhanced (2-14 times with respect to its initial amplitude in eighteen subjects) during the course of the prolonged contraction but its frequency did not change.3. The 4-6 Hz and the 8-12 Hz peaks were present simultaneously; it is concluded that the two phenomena are separate entities.4. A step-function mechanical perturbation of the finger generates, time-locked to the stimulus, a train of waves at the frequency of the slow tremor, which can be abolished by local ischaemia. It is proposed that this slow tremor is due to an oscillatory process, possibly involving the reflex arc, but entailing a longer neuronal delay than that responsible for 8-12 Hz tremor.

SUMMARY1. Simultaneous recordings were made from fusimotor axons in the central ends offilaments ofthe masseter nerve, and from masseter and temporalis spindle afferents in the mesencephalic nucleus of the fifth cranial nerve in lightly anaesthetized cats.2. Fusimotor and a-motor units in the masseter nerve were differentiated on the basis of their response to passive ramp and hold stretches applied to the jaw. Spindle afferents were identified as primary or secondary according to their dynamic index after administration of suxamethonium.3. The activity of a given fusimotor unit during reflex movements of the jaw followed one oftwo distinct patterns: so-called 'tonic' units showed a general increase in activity during a movement, without detailed relation to lengthening or shortening, while 'modulated' units displayed a striking modulation of their activity with shortening, and were usually silent during subsequent lengthening.4. Comparison of the simultaneously recorded fusimotor and spindle afferent activity suggests that modulated units may be representative ofa population of static fusimotor neurones, and tonic units of a population of dynamic fusimotor neurones.5. In these lightly anaesthetized animals, both primary and secondary spindle afferents showed increased firing during muscle shortening as well as during lengthening. This increase during shortening is not usually seen in conscious animals and reasons are given for the view that it is due to greater depression of a-motor activity than of static fusimotor activity during anaesthesia.6. The results are discussed in relation to the theories of 'a-y co-activation' and of 'servo-assistance'; and it is suggested that static fusimotor neurones provide a 'temporal template' of the intended movement, while dynamic fusimotor neurones set the required dynamic sensitivity to deviations from the intended movement pattern.

SUMMARY The pregnant therapist is not often encountered in the psychoanalytic literature, and yet my patients were profoundly affected by my pregnancy. The patient described attempted to recreate in the transference the lost, longed‐for symbiotic mother. Identification with the (fantasised) baby was the main form of defence against separation from the idealised mother and awareness of ambivalence. In the countertransference I developed a corresponding form of primary maternal preoccupation. The primary identification with mother is thus potentially available for exploration in a particularly clear form. Also outlined are some of the countertransference difficulties to be encountered.

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