is designated as the type genus. In general the name of the family is formed from the name of the type genus by affixing the suffix -aceae to the stem of the generic name. The word is plural. Among bacterial families commonly recognized are Bacillaceae, named from its type genus, Bacillus, Pseudomonadaceae from Pseudomonas, Spirochaetaceae from Spirochaeta, Actinomycetaceae from Actinomyces and Spirillaceae from Spirillum.
(4) Order. An order is a group of related families. It is usually named by substituting the suffix -ales for -aceae in the name of the type family. Among ordinal names that have been used in bacteriology are Actinomycetales, Spirochaetales, Myxobacterales.
(5) Class. A class is a group of related orders. In this treatise the bacteria are treated as constituting the class Schizomycetes in Division I., Protophyta, of the plant kingdom.
(6) Other categories. Other categories or ranks of names are used for higher groups. Sometimes families are divided into sub-families, these into tribes, these into subtribes, and these finally into genera.
How to identify an organism by name. One of the purposes of this Manual of Determinative Bacteriology, as noted previously, is to facilitate the finding of the correct scientific name of a bacterium. It is well, however, to note some of the reasons why this result, the identification of an unknown culture, may not eventuate. Among these the following may be listed:
(1) The unknown organism awaiting identification by the investigator may possibly be one which has never been named; or, if named, perhaps was inadequately described. Of course it will not be listed in the Manual. Little effort on the part of bacteriologists has been devoted to describing or naming bacteria except as they have been found to have some economic significance or to possess some striking or unusual characteristics. There are quite probably many times as many species of unknown bacteria as have been described and named. Such unknown species are all about us. It is not surprising, therefore, if one sometimes encounters undescribed species. When such unnamed species are found, particularly if they are of economic importance or are related to such forms, it is highly desirable that they should be adequately described and named, and the results published and made accessible.
(2) The unknown organism may have been described and named in some publication, but the description and name have been overlooked in the preparation of the Manual. Perhaps the description has been so inadequate or incomplete that it has not been possible to place it in a satisfactory classification. It should be noted that the number of species that have been described is so great that no one individual can know them all. Progress in classification comes about largely as the result of the work of specialists in particular groups. Unfortunately most groups of bacteria have not been adequately monographed. It is evidently the function of a Manual such as this to draw largely upon the work of those who have published monographs covering special groups of bacteria and to supplement their achievements as far as possible by a necessarily less satisfactory consideration of the unmonographed groups. It is clear that the fact that an
