MORPHOLOGICAL AND CULTURAL CHARACTERS. 1 15 



seized with forceps, dried high over the flame, and treated as an 

 ordinary cover-glass preparation. In this way very characteristic 

 appearances may sometimes be noted and preserved, as in the 

 case of the anthrax bacillus. The colonies on a plate having 

 been classified, a microscopic examination of each group may be 

 made by means of cover-glass preparations, and tubes of gelatin 

 and agar are inoculated from each representative colony. Each 

 of the colonies used must be marked for future reference, pref- 

 erably by drawing a circle round it on the under surface of the 

 plate or Petri's dish with one of Faber's wax pencils, a number 

 or letter being added for easy reference. 



The general lines along which observation is to be made^ in 

 the case of a particular bacterium may be indicated as follows : — 



1 . Microscopic Appearances. — For ordinary descriptive pur- 

 poses, young cultures, say of 24 hours' growth, on agar should 

 be used, though appearances in older cultures, such as involu- 

 tion forms, etc., may also require attention. Note (i) the form, 

 (2) the size, (3) the appearance of the protoplasmic contents, 

 especially as regards uniformity or irregularity of staining, 

 (4) the method of grouping, (5) the staining reactions. Has it 

 a capsule } Does the bacterium stain with simple watery solu- 

 tions } Does it require the use of stains containing mordants .' 

 How does it behave towards Gram's method .■■ It is important 

 to investigate the first four points both when the organism is in 

 the fluids or tissues of the body and when growing in artificial 

 media, as slight variations occur. It must also be borne in mind 

 that slight variations are observed, according to the kind and 

 consistence of the medium in which the organism is growing. 

 (6) Is it motile, and has it flagella .' If so, how are they 

 arranged .'' (7) Does it form spores, and if so, under what 

 conditions as to temperature, etc. 1 



2. Growth Characteristics . — Here the most important points 

 on which information is to be asked are, What are the charac- 

 ters of growth, and what are the relations of growth (i) to tem- 

 perature, (2) to oxygen .? These can be answered from some of 

 the following experiments : — 



^ The student is asked to consult the recommendations of the Bacteriological 

 Committee of the American Public Health Association, and also Chester's " A Manual 

 of Determinative Bacteriology," where much greater detail is given than is permissible 

 within the size and scope of this work. 



