IDENTIFICATION OF ORGANISMS 135 



or be present only at one stage of the infection. In 

 addition to the microscopical examination, cultures must 

 be made aerobically and anaerobically on various media, 

 those media being chosen which will probably be suitable 

 for the growth of the organism present in the particular 

 condition (see p. 93). In addition, it will in most cases 

 be advisable, and in all safer, in order to isolate the 

 various species, to make plate cultivations or modifica- 

 tions thereof (p. 99). Having obtained pure cultivations, 

 it will be necessary to determine the species of organism, 1 

 if it has been previously isolated and described, or to 

 give a careful description of it, if it be a new one, for 

 the use of subsequent investigators. In the identification 

 or description of an organism all the following features 

 should be carefully noted : 



1. The morphology of the organism under various conditions, 

 its size, form, and motility, the presence of flagella, and their 

 number, arrangement, and character. 



2. The presence or absence of spore formation, its nature, the 

 conditions under which it occurs, and any peculiarities in the 

 germination of the spores, and their size and location in the cell. 



3. The peculiarities of staining, and the staining reaction with 

 Gram's and the Ziehl-Neelsen methods. 



4. The characters of the colonies in gelatin, agar, and other 

 media, both surface and deep. 



5. The characters of the growth on a variety of culture media 

 at different temperatures for example, for a pathogenic organism, 

 on blood-serum, agar, and gelatin (surface and stab cultures), in 

 broth and on potato ; liquefaction or not of the gelatin ; the 

 growth in milk, with or without curdling, and the reaction therein ; 

 and the fermentation reactions on carbohydrates, glucosides, 



1 The descriptions of a large number of species of bacteria have been 

 collected and tabulated in convenient form by Chester in A Manual of 

 Determinative Bacteriology (Macmillan and Co., 1901). The terms he 

 suggests for describing bacterial growths, etc., might well be adopted by 

 bacteriologists. A committee of the Society of American Bacteriologists 

 has drawn up an elaborate chart for the description of species of organisms. 



