92 MICRO-ORGANISMS AND DISEASE [chap. 



favourable conditions of temperature can rapidly and 

 strikingly multiply, there are bacteria which under ordinary 

 conditions live on rich albuminous food and for their 

 multiplication require a comparatively large amount of 

 albuminous matter. Of this nature are most pathogenic 

 bacteria, for their natural breeding-ground are the animal 



Fig. i6. — Stab-cultivation in Gelatine of the Liquefying Bacillus 

 Radicicola. 

 Natural Size. 



tissues, and the preparation of all our culture media 

 previously described is based on this fact. 



All nutritive media must contain salts (sodium or po- 

 tassium salts), in some cases the addition of particular salts 

 (nitrates, phosphates) enhances the growth. Some bacteria 

 require other special additions — e.g. grape sugar in the case 

 of bacillus of Koch's malignant oedema, bacillus of 



