the duct 31 in a preferred form this seal is arranged by o rings 33 which are engaged on the rod and which bear against the wall of the bore 2 so that longitudinal or rotatory movement of the rod will not allow fluid to escape the diaphragm may be inflated for instance by passing an inflation media such as a sterile saline solution air or the like under pressure through the one way valve which can be manipulated when required to deflate the diaphragm although the particular method of inflating the diaphragm by means of the one way valve and the duct 31 are described it is to be understood this is one form only of a suitable method of inflating and deflating the diaphragm and other arrangements which will provide the desired effect can also be employed with reference to fig4 a preferred form of the surgical apparatus comprises a housing 1 having a bore 2 containing a rod 3 the rod 3 contains a gas channel 36 which extends substantially through the center of the rod 3 the apparatus further comprises a nipple 34 for gas entry and a valve means 35 which controls the flow of gas into the gas channel 36 as shown in fig4 both the nipple 34 and the valve means 35 are present at the end of the rod 3 which is distal the diaphragm 14 end of the apparatus the gas channel 36 exits the rod 3 via an opening 37 which is situated adjacent.