SOURCE: Germanic */s/
OE /s/ had two different realizations, or allophones, depending upon its phonetic environment.
1. Voiceless alveolar fricative--initially or in the vicinity of voicless phonemes. Example: sæ "sea."
REFLEX: ME /s/
2. Voiced alveolar fricative--when surrounded by voiced phonemes. Example: risan "rise."
REFLEX: ME /z/