1. Embryonic chick and rat tissues preserved at temperatures ranging from –7° to +20° C. live longest at about +6° C. The duration of life under the most favorable conditions is less than twenty days.
2. The kind of isotonic medium used,—plasma serum, Ringer solution, or normal salt solution,—does not appreciably influence the period of survival. The quantity of medium in proportion to tissue is similarly without marked effect.