Sentence:  [http://books.google.com/books?id=fb3gfJbhL7UC&pg=PA29&dq=call page 29]: I took general-surgery <WSD>call</WSD> at Bossier Medical Center and asked special permission to take general-medical <WSD>call</WSD>, which was gladly given away by the older staff members: .... You would be surprised at how many surgical cases came out of medical <WSD>call</WSD>. / [http://books.google.com/books?id=fb3gfJbhL7UC&pg=PA206&dq=call page 206]: My first night of primary medical <WSD>call</WSD> was greeted about midnight with a very ill 30-year-old lady who had a temperature of 103 degrees. 
Meaning of the word marked with <WSD> tags:  A work shift which requires one to be available when requested (see on call).