94 A MANUAL OF BACTERIOLOGY 



may be used. For organisms of fermentations beer- wort, 

 grape or fruit juice, and carbohydrate solutions will 

 probably prove most serviceable, while for the nitrifying 

 organisms saline solutions, etc., must be employed (p. 35). 

 Some of the organisms of milk will grow only in milk or 

 media containing milk products. A considerable number 

 of the common saprophytic bacteria of air, soil and water, 

 etc., will develop in the ordinary nutrient agar, gelatin 

 and broth. 



If a mixture of organisms be present, isolation of the 

 individual species may be difficult and complicated. Plate 

 cultures, either in Petri dishes, etc. (p. 97), or in tubes 

 (p. 99), will then usually give the best hope of success. 

 Aerobic and anaerobic cultivation should in all cases be 

 employed. Occasionally the dilution method may be 

 employed (see below). 



In some instances single-cell cultures must be made use 

 of (see p. 100). 



Various devices will sometimes aid isolation. Thus 

 aerobic and anaerobic cultivation will separate the strict 

 aerobes and the strict anaerobes. If sporing and non- 

 sporing forms be present, the former may be separated 

 from the latter by heating the material to 80 C. for 

 fifteen to thirty minutes ; the heating kills most non- 

 sporing forms but does not affect the vitality of spores. 



To separate a pathogenic organism from non-pathogenic 

 forms, inoculation into a susceptible animal may succeed. 



The use of " selective " culture media may be of service 

 in some instances. This method is largely employed, 

 for instance, for the isolation of the typhoid-colon group 

 from the faeces, such media as the Conradi, malachite 

 green, and bile-salt being utilised. 



Germicidal agents are occasionally employed. Thus 

 antiformin will destroy all or most of the organisms in 

 tuberculous sputum, except the tubercle bacillus. 



