Injection is a reaction in which a hole in a regular spaceship stream is filled partially or fully by adding a new spaceship or signal of the same type without affecting the existing spaceships in the stream. Depending on the period of the stream, different mechanisms can be used. For adding a spaceship to an existing multi-lane convoy, see inserter.
For large period glider streams, simple reactions such as LWSS-LWSS bounce and LWSS-glider bounce suffice. A large number of Herschel-based edge shooters and transparent conduits are also known, for example the NW31 Herschel-to-glider converter and the Fx119 inserter.
Shown below is an injector found by Dave Buckingham that can fill a hole in a p15 glider stream:
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RLE: here Plaintext: here
For very low-period glider streams, a GIG is a much more efficient insertion method, in the sense that fewer synchronized signals are needed. However, it has been shown that colliding gliders can complete an insertion even into a single-glider gap in a period-14 stream.