Well, I'm a little puzzled by that construction 'à consister à...' --- surely it ought to have been 'a consisté à...'? Or am I missing something elementary here?!
Anyway, be that as it may, I'm sure it does mean "insertable bodies" in terms of the basic sense --- certain special types of transformer DO have more-or-less removable elements; however, I'm afraid I can't give you any inkling as to the more correct technical term...

Maybe this info is some help, I hope you find it OK

--------------------------------------------------
Note added at 51 mins (2004-08-05 14:16:43 GMT)
--------------------------------------------------

Well, a bit of Googling revealed the use of an \'LVDT\' type transformer in come degree of relation to \'graphitization\', so if this might be the type of transformer involved, it has a movable armature or core that is inserted into it --- maybe this is what is being referred to?

Try this ref. (and many more) to find out about these trafos., maybe this will lead you in the right direction!

Construction. Typical Linear Variable Differential Transformer (LVDT). The physical construction of a typical LVDT consists of a movable ...
www.efunda.com/designstandards/ sensors/lvdt/lvdt_theory.cfm