50 OUTLINES OF BACTERIOLOGY 



In the case of aerobic bacteria, viz. those that can grow only 

 when oxygen is supplied to them, growth will take place at the 

 surface. In the case of anaerobic bacteria, which cannot thrive 

 when supplied with oxygen, growth will take place only along 

 the stab. 



(2) Colour, size, and shape of growth on surface. 



(3) Whether liquefaction of gelatine takes place. This takes place 



in various ways ; these should be carefully noted. 



(4) If liquefaction takes place, the sediment must be noted, its 



colour, and amount of deposit. Also, if the sediment is absent, 

 whether there are any particles held in suspension in the 

 liquefied gelatine. 



(5) Whether gas is developed. This is a valuable characteristic 



when it occurs. Thus, by this means, Bacillus coli communis 

 is easily distinguished from Bac. typhosus, although similar 

 in several other respects. 



(6) Microscopically the size, shape, and motility of the cells. 



(7) If growth is along the stab, whether indicated as a continuous 



line, or as a series of dots. 



4. Gelatine Shake-cultures. Prepared in the same way as No. 3, 

 only inoculation is effected when the nutrient-gelatine is in a liquid 

 state. The same points are to be noted as in No. 3. 



5. Agar Slope-culture. The agar is allowed to solidify in the sloping 

 condition (Fig. 63). There should always be a small amount of water 

 at the bottom of the slope. The bulk of the observations are usually 

 made on this form of culture. These points are noted : 



(1) Colour of growth on surface. 



(2) Size, shape, and motility of the cells after G hours, 15 hours, 



24 hours, 48 hours, 72 hours, 5 days, and 10 days growth on 

 the nutrient-agar. If the material consists of spores only, 

 the life-history from spore-germination to spore-formation will 

 usually be traversed in about 3 days, but under different 

 circumstances this period may be prolonged or shortened. 

 The whole life-history may be passed over in one day under 

 certain external conditions at present unknown. 



(3) Any changes in the condensed water at the bottom of the 



slope. 



(4) Any special peculiarity in growth, whether thick or thin or 



mucilaginous. These, however, are not of much value because 

 of the extreme variability of growths. 



(5) Presence or absence of fluorescence. 



