It is assumed that the reader of this Manual has some knowledge and experience of bacteriology and of elementary chemistry and that the basic principles including those of laboratory safety are understood. Thus, though many other essential details are given in the Appendices, how to determine the pH value of a medium, or how to make a normal or molar solution, is not described; nor are details given about how to use anaerobic jars or microscopes. Serology is not discussed but methods commonly used in the preparation of extracts for grouping streptococci are described as the Lancefield serological groups are referred to in Table 6.3b. Details of sterilization temperatures and times are also given as these so-called standard procedures still vary from one laboratory to another.

This Manual is intended to help those who have isolated a bacterium and want to identify it. The methods used by clinical bacteriologists to isolate organisms from specimens sent to the laboratory are not described as to do so would be to enter everchanging fields, and our recommendations might well be out of date. We stress, however, that before identification of any organism is attempted, it must be obtained in pure culture. Some advice on how to recognize that a culture is impure, and on the steps to be taken to purify it, is therefore given.