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An aspect of bacteriophage morphology which never fails to excite speculation is the function of that tail which is characteristic of most of the T-bacteriophages and, so far as is known, of all other bacteriophages. Until recently nothing has been known about the tail, and there has been no reason to call one end a tail and the other a head, except for the obvious similarity in appearance to higher organisms, such as tadpoles. The most recent work indicates (Goldwasser and Putnam, 1951) that the tail is not an organ of locomotion, but even this has been the subject of much dispute. It has been reported recently (Herriott, 1951 and Hershey and Chase, 1952) that the entire shell of the phage is composed of protein. In the last few months a greatly renewed interest in the tails has been engendered by the publication of electron micrographs apparently showing that the T2 and T4 phages adsorb to the bacterial host by their tails (Anderson, 1952), and by the statement (Hershey and Chase, 1952) that on invasion the nucleic acid material inside the phage shell enters the bacterium and leaves the protein ghost with attached tail outside. Obviously speculation that the bacteriophage tail serves a function of any sort, such as in the adsorption mechanism, has had to take cognizance of the apparent lack of tails of two of the well known series of T-phages; namely, T3 and T7. These phages are related serologically to each other, but not to the other five T-phages, and have long been described as spherical and tailless (Anderson, 1949; Benzer et al., 1950). The recent development of a new technique of freeze-drying specimens for electron microscopy (Williams, 1953) has made it enticing to reexamine the tailless phages for detailed morphology under conditions which lead to a minimum of preparative distortion.

DETAILS OF FROZEN-DRIED T3 AND T7 BACTERIOPHAGES AS SHOWN BY ELECTRON MICROSCOPY