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 

 ]\Ianual 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 ne- 

 cessitating resort to the original literature. When those prevailing are inad- 

 equate, 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 or- 

 ganism 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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