PREPARATION OF NUTRIENT MEDIA. 6 1 



during their growth, and free from contamination, it 

 is only necessary to thin out the cultivation, and to 

 protect the plates from the air. The slower growth 

 of the micro-organisms in solid media, and the 

 greater facility afforded thereby for examining them 

 at various intervals and stages of development, is 

 an additional point in favour of these methods ; and 

 the characteristic macroscopical appearances so 

 frequently assumed are, more especially in the case 

 of morphological resemblance or identity, of the 

 greatest importance. The colonies on nutrient 

 gelatine (examined with a low power) of the bacillus 

 anthracis and proteus mirabilis ; the naked eye 

 appearances in test-tubes of nutrient gelatine of the 

 bacillus of mouse-septicaemia (Figs. 38, 39), and of 

 anthrax (Fig. 37), and the brilliant and curious 

 growth of micrococcus indicus upon nutrient agar- 

 agar (Plate II., Fig. i), may be quoted as examples 

 in which the appearances in solid cultivations are 

 pathognomonic. 



SOLID MEDIA. 



(A) PREPARATION OF STERILE, GELATINE-, AND 

 AGAR-AGAR-PEPTONE-BROTH. 



Sterile Gelatine-Peptone-broth, or Nutrient 

 Gelatine, is prepared as follows : Take half a 

 kilogramme of beef (one pound), as free as possible 

 from fat. Chop it up finely, transfer it to a flask 

 or cylindrical vessel, and shake it up well with a 



