120 BENZER ET AL. 



distilled water. Small amounts of non-transparent material on the 

 bottom of the centrifuge tube are removed mechanically. 50 g of moist 

 bacteria yield about 25 g of sediment, the dry weight of which amounts 

 to only about 10% of the dry weight of the bacteria. 



Morphology* 



Electron micrographs show that the sediment prepared by the 

 method described here consists entirely of bacterial cell walls, which 

 are crumpled up and folded to give completely flat, almost circular 

 particles of rather uniform size. The uniformity of the material is 

 confirmed by studies in the ultracentrifuge and by electrophoresis, 

 where sharp boundaries and no indication of major impurities were 

 seen. 



If the preparation is made from bacteria, which have begun to 

 come into the lag phase, one obtains not only this material but in addi- 

 tion bacterial cell walls which did not fold up to give disk shaped par- 

 ticles but retained the oblong shape of the coli cell. This is also evident 

 macroscopically by the strong streaming birefringence shown by this 

 fraction which can be separated from the usual folded membranes by 

 differential centrifugation. The stretched membranes require a much 

 longer time to be spun down. Morphological details appearing on 

 electromicrographs shall not be described here. It seems to be clear 

 that the particles — stretched or folded — are nothing but empty col- 

 lapsed bags with extremely thin walls. 



Anti-phage activity 



Both folded and stretched membranes, suspended in concentrations 

 corresponding to bacterial cultures of 10^ - 10^" bacteria per cc adsorb 

 phages T2, T4, and T6 approximately as fast as normal living bacteria. 

 The rates depend on the concentration of the membranes as they do on 

 the bacterial concentration. The cof actor requiring strains of T4 and T6 

 are adsorbed by the membranes in broth, or buffer plus tryptophan, but 

 not in buffer alone. The adsorption capacity of the membranes for T6 

 seems to be smaller than that for T4 and T2 and it also seems to be de- 

 pendent upon the age of the culture from which they were prepared. 

 Very slight adsorption occurs with T3 and T7, none with Ti and T5. 



Electron micrographs of mixtures of T2 and membranes, which 

 were kept overnight in the ice box, seem to indicate that the membranes 



*The electron micrographs were taken in collaboration vnih Dr. R. F. Baker of the 

 University of Southern California. 



