Each is regenerated separately, then remixed during the regeneration process. Some studies have revealed that optic nerve fibers can be regenerated in postnatal rats. The thread made from the regenerated cellulose is washed to remove residual acid. The catalyst should be regenerated or replaced as needed. The sulfuric acid is regenerated and recycled to the leaching step. The bisulfide anion is subsequently regenerated by heating of the amine sulfide solution. Until recently, it was commonly believed that cardiac muscle cells could not be regenerated. Periodically the macronuclei must be regenerated from the micronuclei. Rhodopsin pigment must be regenerated for further phototransduction to occur. It states that it is possible to be regenerated without baptism, and unregenerated with baptism. Both tails and limbs can be regenerated. The anhydrous salt can be regenerated by heating the hydrates. Skin tissue can be regenerated "in vivo", and "in vitro". In the absence of light, rhodopsin is regenerated. A related technology is flow batteries, in which the fuel can be regenerated by recharging.