Studied about a hundred infants of mothers cared for in penal institutions.  They observed their behaviour during a separation which occurred for nearly three months during which the infants were cared by other mothers or expecting mothers with contact with the natural mother around once a week. They noted that infants during this period  experienced what they called 'anaclitic depression'. They also noticed that, provided it occurred within three months, return of the mother permitted remission of this condition.