Maintenance of Bacterial Cultures

^ In most laboratories in the North American Continent and in England, the older methods of Maintaining bacterial cultures by constant subculturing in suitable media have of recent years been largely superseded by the method of rapid freezing and dehydration in vacuo. As early as 1896, Martin suggested the possibility and Procedure involved in the preservation of guinea-pig complement in the dried state. Noguchi, in 1907, dried complement and amboceptor on filter paper. Shackell, in 1909, dried pomplement in the frozen state and showed that *t could be preserved for months. Karsner and Collins, in 1919, applied Shackell's method for the preservation of various sera and, in 1923, Hartley and his associates reported the dehydration of complement by distilling off the H20 in vacuo. In 1931, Craigie dried complement in the frozen state by means of a vacuum desiccator and more recently Elser and his co-worker (1936) showed conclusively that biological Materials could be dehydrated from the frozen state. This method was admirably developed by Flosdorf and Mudd (1935) in the University pf Pennsylvania and resulted in their dry ice jyophile apparatus' by means of which many biological materials could be preserved for several months without any detectable deterioration. The same investigators, in a later communication, in 1938, described a new process where the condensation of water vapour in a low temperature bath (dry-ice methyl cellosolve Mixture) is replaced by the use of an inexpensive chemical desiccant (the Cryochem process). The method has been very profitably employed for the preservation of various anti-toxins, guinea-pig complement, human plasma for purPoses of transfusion, normal and convalescent human sera, enzymes, viruses, bacteria and Miscellaneous proteins. . The procedure and apparatus to be described M this communication are a modification of the Cryochem process' described by Flosdorf and ^ludd in 1938. This has been successfully emPloyed in the preservation of bacterial cultures though it can be used for preservation of sera, Protein solutions andother labile biological Materials with equal success.