INTRODUCTION
Suggestions for the Use of the Manual In Classifying Unknown Organisms
No organism can be classified before its morphological, cultural, physiological and pathogenic characters have been determined through a detailed study.
The characters used in the keys to orders, families and genera may ordinarily be determined by the use of a dozen or more of the procedures described in the Manual of Microbiological Methods issued by the Committee on Bacteriological Technic of the Society of American Bacteriologists. More complete examinations are required in special cases to identify and to describe individual species necessitating resort to the original literature. When those prevailing are inadequate, new criteria are desirable. This desideratum extends to some higher taxa to achieve more exact and distinctive definitions.
It is urged that beginning students be taught all of the techniques necessary for the identification of species in the hope that the taxonomic work of the future may be placed on a satisfactory basis.
After a complete study of the characters of the organism has been made, either of two courses may be followed. (1) Use the Keys in the body of the text as explained below. These follow what are believed to be the natural relationships that exist between various groups of bacteria. (2) The beginning student may, however, find the artificial key at the back of the Manual to be more helpful than the natural keys in determining the identity of an unknown culture.
In all cases it should be kept in mind that many descriptions of species of bacteria are not mentioned in this Manual. Failure to find agreement between an unknown culture and any of the descriptions given in this Manual does not prove that the unknown culture represents a species that has never been studied and described.
If the student wishes to follow through the natural keys he should turn to page 33 and ascertain first in which order the organism belongs. When the order has been ascertained, turn to the page of the Manual on which the key to that order is given. In this key ascertain the family or sub-family to which the organism belongs.
When the family has been determined, again refer to the page of the Manual on which the key to that family is given. In this key ascertain the tribe to which the organism belongs.
When the tribe has been determined, again find the page of the Manual on which the key to the tribe is given. In this key ascertain the genus to which the organism belongs.
When the genus has been determined, again refer to the page of the Manual on which the key to that genus is given. In this key trace out the species under investigation.
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