48 MANUAL OF DETERMINATIVE BACTERIOLOGY 



pathogenic spore-bearing anaerobes by the English Commission, by Wein- 

 berg, and by others, of the red, rod-shaped bacteria by Hefferan and by 

 Breed, of the actinomycetes by Waksman and by Lieske, of the root nodule 

 bacteria of legumes by Fred and his co-workers, etc. Unfortunately most 

 groups of bacteria have not thus been monographed. It is evidently the 

 function of a manual such as this to draw largely upon the work of the 

 monographers, and to supplement their achievements as far as possible by 

 less satisfactory consideration of the unmonographed groups. 



It is clear that because an organism cannot be identified from this text 

 is not proof that it has not been described and named. The species most 

 closely related may be determined, then the literature searched carefully 

 for species described still more closely related or perhaps one identical. 



(3) It is possible, of course, that an error has been made in the selection 

 of the correct name. It is desirable that users of these keys and descrip- 

 tions should be familiar with the rules governing the correct choice of names, 

 and make suitable corrections where needed. 



Steps in determining the name of an organism. The steps in the identifi- 

 cation of an uiikno\\Ti organism are usually the following : 



(1) Preparation of an adequate description of the organism. 



(2) Knowledge of construction and use of keys. 



(3) Determination of order, family and genus by use of key. 

 Preparation of description of organism. Before attempting to determine 



the name of an ''unknown" organism an adequate description is essential. 

 Just what characteristics must be emphasized depends upon the group in 

 which the organism falls. It is desirable that the knowledge of the charac- 

 ters of the unknown be as complete as possible. 



Use and construction of keys. An exceptionally clear and satisfactory 

 discussion of the making and use of keys and synopses is given by Hitch- 

 cock (Descriptive Systematic Botanj^ New York, 1925, p. 104). Anyone 

 planning to monograph a group is advised to read this. He states: "A key 

 is an orderly arrangement of a series of contrasting or directly comparable 

 statements, by which groups of the same category may be distinguished 

 and indicated or identified," and "A key is primarily a mechanical device 

 by which one may arrive at the name of the ultimate member of the group." 

 In general the keys used in this Manual are dichotomous, that is, the suc- 

 cessive divisions are in twos, differentiation being into two contrasted 

 groups. 



Determination of order, family and genus hyuse of keys. The method of 

 doing this is discussed in the introduction beginning on page 1 . 



