INTRODUCTORY I44-II 



should not be contented with one or two observations, but should 

 study several transfers and should follow up each of them day by day 

 for about a week. When changes are observed, a careful study 

 should be made to learn whether they indicate morphologic variation, 

 dissociation, or merely contamination. In making special staining 

 tests, like the Gram stain, several determinations should be made on 

 separate transfers of the culture and at different ages, because there 

 are species that vary in their staining reactions, and such variation 

 cannot be detected by single determinations. As a check on the 

 technic, a known positive and a known negative culture should be 

 included in the study. For example, when making a Gram stain, it 

 is good practice to place on the slide, beside the culture under study, 

 a smear containing a mixture of a known Gram-positive and a known 

 Gram-negative organism (which differ markedly in morphology). 

 Then it is possible to observe whether the expected results are ob- 

 tained with the known cultures, and thus to have some degree of con- 

 trol on the technic. 



Identification: After recording the characteristics of an organism, 

 the next step is identification, if possible, with a previously described 

 species. This should never be attempted until at least six repre- 

 sentative strains of the unknown organism isolated from more than 

 one source, if possible, have been studied. No rules can be given for 

 identifying the culture. Descriptions of bacteria are scattered so 

 widely through the literature and vary so greatly in their form that 

 identification is often extremely different. Bergey's Manual of 

 Determinative Bacteriology is a great help; but it is usually neces- 

 sary to go back to original descriptions and often to secure transfers 

 of authentic strains before certain identification can be made. Diffi- 

 cult as this procedure is, no one is justified in naming a new species 

 of bacteria until a comprehensive search through the literature of 

 species already described has been made. Frequently it is necessary 

 to refer in some publication to a previously described species on the 

 basis of such an identification as this. In this case it is important to 

 state in the publication whether or not an authentic strain of the 

 species has been obtained for comparison; if so, from where obtained; 

 if not, what published description of the species was followed in 

 making the identification. As to a name to use for such a species 

 one may follow the original author's nomenclature or may give it the 

 name employed in some modern system (e.g. Bergey). Whatever 

 name is chosen no confusion will result it if is accompanied by the 

 name of the original author of the specific name and by that of the 

 one making the combination of generic and specific names. Thus, 



