Attendance of witnesses may be dispensed with.

When the person whose evidence may be required is unable, from sickness or infirmity, to attend before the officer issuing the summons, or is a person whom by reason of rank or sex it may not be proper to summon, the officer issuing the summons may, of his own motion, or on the application of the party whose evidence is desired, dispense with the appearance of such person, and order him to be examined by a subordinate deputed by such officer for the purpose.