A housing (12； 112, 212) receives a syringe and includes a return spring (26；126, 226) for biasing the syringe from an extended position in which itsneedle (18； 118, 218) extends from the housing to a retracted position inwhich the it does not. A drive spring (30； 130, 230) acts on a first driveelements (32； 132, 232) and a second drive element (34； 134, 234) acts uponthe syringe to advance it from its retracted position to its extended positionand discharge its contents through the needle. The first drive element iscapable of movement relative to the second when the former is acted upon bythe drive spring and the latter is restrained by the syringe (14, 114, 214). Areservoir (48； 148, 248) is defined between the first drive element and thesecond drive element, the volume of the reservoir tending to decrease as thefirst drive element moves relative to the second when acted upon by the drivespring. The reservoir contains a highly viscous fluid and has a vent (44； 144,244) through which the fluid escapes as the volume of the reservoir.
