in this position is held against rotation by the splines 50 on the actuator button in this condition the change in status is registered by the colour change in windows 17 adjacent the dial 16 pushing the actuator button 18 forwardly releases the drive gear 32 so that it rotates with the ratchet drive shaft 24 under the influence of the torsion spring 34 advancing the plunger 44 a counter wheel 54 is mounted concentrically with the drive gear 32 by means of spaced mounting plates 56 which also mount an idler gear 58 which meshes with an inner toothed track 59 on the inside of the counter wheel 54 the plates 56 are angularly fixed with respect to the housing and as the drive gear 32 rotates the teeth 46 trip the teeth of the idler cog 58 which in turn rotates the wheel by a uniform increment to register delivery of a dose and to keep a cumulative count as in seen in fig7 the rear end of the plunger is formed with two lugs 60 which as the plunger reaches its fully extended position engage or move between lugs 62 on the inside of the ratchet drive shaft 24 thereby restricting or preventing further rotation of the ratchet drive shaft relative to the plunger this not only blocks further.