APPENDIX 445 



Host Organisms and Viruses 



Bacteriophages have been recorded for the various groups of 

 enteric bacteria such as shigella, salmonella, proteus aerobacter, 

 vibrio, and escherichia. They are also known for bacilli, staph- 

 ylococci, streptococci, corynebacteria, mycobacteria, and ac- 

 tinomycetes. Phagelike agents are not known for protozoa, 

 algae, yeasts, or molds. Extensive investigations have been car- 

 ried out on certain groups of phages, in particular on the staphy- 

 lococcus phages by Northrop (1939a) and Krueger (1932), sal- 

 monella and coli-dysentery phages by Burnet (1934a), cholera 

 phages by Asheshov, Asheshov, Khan, and Lahiri (1933), typhoid 

 phages by Craigie (1946), and coliphages by Schlesinger (1933a). 



In the United States the most intensively investigated phages 

 are the group of 7 coli-dysentery phages described by Demerec 

 and Fano (1945) and studied by Delbriick, Luria, Hershey, 

 Cohen, Beard, Anderson, and many others. All methods de- 

 scribed here have been tested on this group of phages but are 

 more generally applicable. The work has been reviewed by 

 Delbruck (1946a, b). 



Media 



In work with strain B of Escherichia coli and its phages, the 

 most generally useful medium is nutrient broth which contains 

 8 g. of Difco nutrient broth and 5 g. of NaCl/liter of water. 

 To this is added 1 5 g. of Difco agar/liter to make nutrient agar 

 for plates. For most phage work the agar in the plates should 

 be fairly deep, the requirement being about 30 ml. of nutrient 

 agar /Petri dish. The plates should be stored in an incubator at 

 37 ° G. overnight to dry them before use. Otherwise water of 

 condensation will cause coalescence of plaques and ruin the 

 plates for quantitative use. For preparation of agar slants for 

 routine cultivation of the host organism and its mutants, 2 

 per cent nutrient agar is most suitable since bacteria from such 

 a slant seem to be more readily dispersed in a uniform suspen- 

 sion. 



