120 A MANUAL OF BACTERIOLOGY 



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, alcohols, 

 etc. ; the nature of the gas, if any, formed therefrom, and the 

 H:C0 2 ratio. 



6. The behaviour towards oxygen is it aerobic or anaerobic ? 



7. The range of growth at different temperatures. 



8. The reducing power by growing in litmus broth which becomes 

 decolorised, or by the formation of nitrites in a solution containing 

 nitrates. 



9. The production of indole with or without nitrites. 



10. The production of pigment and the conditions under which 

 it occurs. 



11. The pathogenic action on various animals if it be a disease 

 germ, or the changes which it produces if it be an organism connected 

 with other conditions. 



12. The chemical changes which it induces. 



13. The thermal death-point and the action of germicides and 

 antiseptics upon it (see Chapter XXII). 



For descriptive purposes, " standard " culture media 

 should always be employed, and the acidity or alkalinity 

 of the medium stated (p. 64). 



It must never be forgotten that under cultivation the 

 properties of organisms may be considerably modified, and 

 due allowance must be made for this. For example, 

 pathogenic organisms may lose their virulence more or 

 less completely, pigment production be lost, and fer- 

 mentive action modified (see also p. 6). 



To obviate these difficulties the organisms should be 

 cultivated under as nearly natural conditions as possible 

 and sub- cultivation avoided so far as can be. No general 



