All samples were placed on the surface of a copper specimen holder (16 29 1.5 mm). A small amount of the cryo-adhesive ‘Tissue Tek’ was applied to the mounting surface of the specimen holder prior to placement of the samples. Holders containing specimen materials were rapidly placed on the surface of a square brass metal tube pre-cooled in liquid nitrogen ( 196 C) within a styrofoam box. This process of contact freeze immobilization was performed on all samples used in the experiment. Numbered, frozen sample holders were placed into the same square brass tubing for storage in a liquid nitrogen storage dewar until removal for observation.