Gerdy later introduced a method whereby invagination of the scrotum by means of the left index finger into the inguinal canal as far as possible followed by passage of a long needle armed with waxed silk through the invaginated skin, through the tendon of the external oblique, and exiting above Poupart’s ligament, followed by application of ammonia to scarify and ultimately obliterate the canal.
The difficulty and injuries encountered with Gerdy’s unguarded needles induced Zeis to introduce a guarded needle that could be employed with the utmost speed while avoiding the operator’s finger.  The same acrid substances were use to fix the invagination and likely failed over a short time.