Serological Responses and Clinical Reactions to Influenza Virus Vaccines

necessary to lay down the sequences of movement in advance.It is not known whether this neurocellular atrophy is a direct result of the ageing process or whether it is based on ischaemia.Biemond (1951) found disappear- ance of Purkinje cells as a minimal result in some cases of basilar artery thrombosis, and suggested that " slight interference with the circulation in the cerebellum mav lead to a local and perhaps also a more diffuse disappearance of the Purkinje cells."These observa- tions are particularly relevant in view of the fact that no less than 50% of the whole sample and 60% of those having drop-attacks were unable to throw their head back without immediate symptoms.Reasons have already been adduced for the view that this is based on temporary obstruction to one or both vertebral arteries facilitated by senile cervical osteoarthritis, and it fits in well with Kremer's (1958) suggestion that drop- attacks are based on transient changes in the blood- supply to the brain-stem.Relative ischaemia in the territory supplied by the vertebral and basilar arteries might also underlie the high incidence of abnormal plantar responses, and much of the vertigo of which old people complain so bitterly may have the same origin.It is suggested, therefore, that the general insecurity of postural control and the liability to fall which are characteristic of old age are based ultimately on a decline in the number of nerve cells in the brain-stem, cerebellum, and other centres-below that available for the maintenance of normal postural function in earlier life.The adverse effects of this cellular poverty will inevitably be accentuated by interference with the blood supply to the region which, in two ways, is particularly apt to happen in old age-by the liability of the vertebral arteries to temporary obstruction and the general proneness to phases of hypotension based on postural and other causes.Many intriguing problems remain; the drop-attack remains a remarkable event-from its instantaneous onset to its apparent path of recovery in some cases by the initiation, through pressure on the soles of the feet, of a reflex which seems hitherto to have belonged more to the province of neurophysiology than of clinical medicine.Therein, however, lies one of the fascinations of old age as a clinical study, for these phenomena have been uncovered because at this stage of life Nature resembles the engineer who may release the unexpected when he tests his materials to destruction.