law: 35. Employment of criminal prisoners.
  (1) No criminal prisoner sentenced to labour or employed on labour at his own desire shall, except on an emergency with the sanction in writing of the Superintendent, be kept to labour for more than nine hours in any one day.
  (2) The Medical Officer shall from time to time examine the labouring prisoners while they are employed, and shall at least once in every fortnight cause to be recorded upon the history-ticket of each prisoner employed on labour the weight of such prisoner at the time.
  (3) When the Medical Officer is of opinion that the health of any prisoner suffers from employment on any kind or class of labour, such prisoner shall not be employed on that labour but shall be placed on such other kind or class of labour as the Medical Officer may consider suited for him.