SUMMARYOne hundred and thirty-nine strains of Serratia marcescens were investigated for bacteriocin and phage production. Two types of bacteriocins were detected. Group A were all active on serratias and were produced by 71 strains. Some of these bacteriocins also attacked Salmonella, Escherichia and Aerobacter strains. They were produced spontaneously in broth, and higher titres were produced by induction with ultraviolet (u.v.) radiation. These bacteriocins are divided into eight subgroups by their spectrum of activity and resistant mutants of indicator strains. Group B bacteriocins are not active on serratias. Their action is restricted to escherichias, hafnias and aerobacters. Mutant bacteria resistant to any one of these B agents are resistant to all other B bacteriocins. The B agents are serologically similar and are produced in broth by 54 strains. They are produced spontaneously and higher titres are produced after U.V. induction. With one exception the B bacteriocins may be identical. Thirty-five strains produced both types of bacteriocins. The A bacteriocins are resistant to chloroform, trypsin and the proteolytic enzymes of certain organisms, are heat-stable and non-dialysable. Group B bacteriocins are heat-labile, nondialysable and inactivated by chloroform and the above enzymes. Agents A and B differ from colicins. Thirty-seven of the strains were lysogenic for Serratia species and 19 of the phages productively lysed Salmonella species. Although overlaps did occur it was always possible to distinguish the bacteriocins from the corresponding temperate phage produced by a strain, by means of their spectra of activity.

the same amotUlt of corticosteroids through their cuticle in either situation on the host. However, they probably ingest more blood when fixed, which may be significant. The relationship between the hormone, maturation, increased defoocation rate and feeding behaviour of the fleas requires further investigation.

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GSSG via the pentose phosphate pa.thway is inadequate, the ability to synthesize glutathione impaired, or the sulphydryl stability of haemoglobin decreased; (e) GSH assumes a vital role when either normal or abnormal erythrocytes are exposed to aromatic catalysts, by helping to absorb the vastly increased oxidative potential, and thus with the aid of the process of methaemoglobin formation to buffer against irreversible damage.It is recognized that this unified concept may fail to account for possible contributory factors. The ideas are put forward in order to direct attention to the selectivity of different forms of oxidant haemolysin, and to emphasize the variable significance of the protective role of GSH in different types of human erythrocyte placed under varying degrees and types of oxidative stress.