GROWTH CHARACTERISTICS. 125 



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 

 purposes young cultures, say of 24 hours' growth, on agar 

 should be used, though appearances in older cultures, such 

 as involution 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 solutions? 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. ? 



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 (i) to temperature, (2) to oxygen? These can be 

 answered from some of the following experiments : 



A. Growth on gelatine, (i) Stab culture. Note (a) 

 rate of growth ; (&) form of growth, (a) on surface, (ft) in 

 substance ; (c} presence or absence of liquefaction ; (d) 

 colour ; (e) presence or absence of gas formation and of 

 characteristic smell; (/) relation to reaction of medium. 

 (2) Streak culture. (3) Shake culture. (4) Plate cultures. 

 Note appearances of colonies (a) superficial, (d) deep. 

 (5) Growth in fluid gelatine at 37 C. 



B. Growth on agar at 37 C. (i) Stab. (2) Streak. 

 Also on glycerine agar, blood agar, etc. Appearances of 

 colonies in agar plates. 



