140 GENERAL BACTERIOLOGICAL DIAGNOSIS 



medium or in its substance, as colonies of the same bacterium 

 may exhibit differences according to their position. The 

 arrangement of the bacteria in a surface colony may be still 

 more minutely studied by means of impression preparations. 

 A cover-glass is carefully cleaned and sterilised by passing 

 quickly several times through a Bunsen flame. It is then placed 

 on the surface of the medium, and gently pressed down on the 

 colony. The edge is then raised by a sterile needle, it is 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, preferably by drawing a circle round it on 

 the under surface of the plate or capsule with one of Faber's 

 pencils for marking on glass, 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 twenty-four hours' growth, on agar 

 should be used, though appearances in older cultures, such as 

 involution forms, etc., may also require attention. Note (1) 

 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 1 Does the bacterium stain with simple watery 

 solutions'? Does it require the use of stains containing 

 mordants'? How does it behave towards Gram's method 1 ? 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 1 If so, how 

 are they arranged'? (7) Does it form spores, and if so, under 

 what conditions as to temperature, etc. *? 



2. Growth Characteristics. Here the most important points 

 on which information is to be asked are : What are the characters 

 of growth and what are the relations of growth (1) to tempera- 



