SUMMARY1. In rats under Nembutal anaesthesia the inferior olive region has been reversibly inactivated by applying a cooling probe to the ventral surface of the medulla. Simple and complex spike activity has been recorded from Purkinje cells of the cerebellar cortex.2. Following cooling of the inferior olive of one side we have observed a remarkable increase of the simple spike activity in all the twenty-two Purkinje cells, showing a disappearance of the complex spike activity.3. In some rats two Purkinje cells were recorded simultaneously from each side of the cerebellar cortex. Following cooling of the left inferior olive the effect on the Purkinje cell was observed only or predominantly on the contralateral cerebellar cortex.4. In a group of animals the inferior olive has been destroyed by 3-acetylpyridine 4-221 days before the recording session. Cooling of the inferior olive region was not accompanied by any significant and consistent increase in the spike activity of presumed Purkinje cells of the contralateral cerebellar cortex.5. These results indicate that the remarkable increase of the simple spike frequency following cooling of the inferior olive region is due specifically to the suppression of the activity of the olivocerebellar neurones.6. Only a small amount of the simple spike frequency increase is attributable to the removal of the post-climbing fibre pause.7. In some lesioned rats recording was made from Purkinje cells, which showed complex spikes due to the few surviving inferior olive cells. In these Purkinje cells cooling of the inferior olive region was accompanied by a disappearance of the complex spike and by a small increase ofthe simple spike frequency of discharge. Such an increase is mainly attributable to the removal of the post-climbing fibre pause.8. These results suggest that a given Purkinje cell is not only under the inhibitory influence of its own climbing fibre, but also of other olivocerebellar neurones, probably through climbing fibre collaterals to the cerebellar cortical interneurones.9. It is suggested that one role of the olivocerebellar system is to exert a powerful tonic inhibitory action on the Purkinje cells and consequently to exert a significant control on the excitability of the subcerebellar centres.

It has been hypothesized that siblings in different positions within the family constellation are subject to varying degrees of stress (1, 2). Owing to this factor, the first-born sibling is not infrequently presented as having significantly greater difficulties in adjustment than the later born (3). Since stress is believed to be an etiological variable in schizophrenia, attempts were made to establish the existence of a definite relationship between sibling position (especially that of the first-born) and the incidence of this disease in a large sample (1). This relationship has, however, never been satisfactorily established (4). In the majority of studies, families of all sizes, as well as families that are most probably incomplete-containing other psychotic siblings, siblings who have died, and so on-are included in the samples. Thus, the conclusions lack consistency, in part at least, because of shortcomings in statistical design or analysis (5). An attempt was made in the study discussed in this report to investigate the hypothesized relationship between sibling position and incidence of schizophrenia in such a way as to minimize the errors mentioned.The data were collected during 1955 and 1956 at Warren State Hospital, Warren, Pennsylvania. The cases studied were restricted to schizophrenic patients with two normal siblings and were drawn from the following sources: the files of such patients present in the hospital for more than 2 years and the files of such patients discharged over a period of 15 years. The information recorded in each file included the age and the sex of the patient and of his siblings, so that ordinal position by sex could be determined. Families containing adopted children or stepchildren, twins, triplets, or siblings who had also been hospitalized for any mental disease were rejected. Also excluded were cases in which a sibling had died before the patient reached his 20th year, or in

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