In order to study certain phases of the life cycle of the snake mite, Ophionyssus natricis (Gervais), it was found necessary to devise some method of isolating individual mites under as nearly natural conditions as possible. Several artificial media, including liquid snake blood and snake blood agar, were tried without success, as the parasites either failed to feed or became bogged down in the media. Another solution was to find some method of isolating the parasites on the natural host in a manner that would permit observation of them. Several methods, employing various designs of celluloid cells, were tried with varying degrees of success and failure. In devising a workable chamber, three main difficulties were encountered. Either the snake host or the mites were killed or, if neither were harmed, the mites were able to escape from the cell. Finally, after many unsuccessful attempts, a chamber, which retained the parasites without harming them or their hosts, was perfected. Celluloid sheeting, celluloid tubing, microscope slide cover glasses, and acetone were the only materials used in the construction of the isolation chamber. A base (Fig. la), 12 mm. square, was cut from a sheet of celluloid; a hole, 7 mm. in diameter, was punched in the center with a paper punch; and four small holes, one in each corner, were drilled with a half-round surgical needle. A ring, 5 mm. in length, was then sliced from a celluloid tube whose inside diameter was 7 mm. and whose