Help appreciated parsing these....
13a. Losing head, alien foe turned on a wolf (5) - AKELA (Wolf)
33a. General direction, briefly, infantry must receive check for disease (6,4) - TRENCH FOOT (Infantry disease)
3d. Some special skill winds prayer period up (5,6) - TRADE SECRET (Special skill)
25d. Insulting term Old Bill received: "dummy"? (7) - PLACEBO (Dummy?)