48 



PRINCIPLES OF BACTERIOLOGY 



FIG. 21 



water is added to bring the fluid up to its original bulk. If the fluid is 

 clear it is put into flasks and tubes and sterilized; if not clear, the white 

 of one or two eggs is added to the fluid after cooling it down to about 

 55 C. After thoroughly mixing the eggs, the bouillon is boiled briskly 

 for a few minutes, its reaction adjusted, and then again filtered and dis- 

 tributed in flasks and put in the Arnold 

 sterilizer for one hour on each of three 

 consecutive days, or in the autoclave 

 for twenty minutes for sterilization. 

 Instead of meat 2 to 4 grams of Lie- 

 big's or some other meat extract are 

 added to each litre of water. For some 

 purposes the extract is as good as the 

 fresh meat, but for others it is inferior. 

 This infusion contains very little albu- 

 minous matter, and consists chiefly of 

 the soluble salts of the muscle, certain 

 extractives, and any slight traces of 

 soluble proteid not coagulated by heat. 

 It is not, therefore, a suitable medium 

 for most bacteria. 



We use this as a basis for the fol- 

 lowing more useful media : 



BOUILLON MEDIA. These consist 

 of meat infusion plus certain sub- 

 stances. 



(a) Peptone or Nutrient Bouillon.- 

 This has the composition: meat infu- 

 sion, 1000 c.c.; sodium chloride, 5 grams; peptone (Witte), 10 grams. 

 Warm moderately and stir until the ingredients are dissolved, then 

 boil for thirty minutes in the Arnold sterilizer or the autoclave and 

 treat as in making meat infusion. For the careful study of bacteria 

 the exact reaction of the media should be carefully determined. For 

 this purpose standard solutions are used with phenolphthalein or 

 litmus as an indicator. This subject will be taken up in detail at the 

 end of the chapter. For water bacteria sodium chloride is omitted and 

 the reaction is made + 1 per cent. 



(b) Sugar Bouillon. To the peptone broth after its completion 1 to 2 

 per cent, of glucose, lactose, saccharose, or other sugars is added. No 

 more boiling than necessary to sterilize should be used after the addition 

 of the sugars, since they become altered by heat. Temperatures higher 

 than 100 C. should never be employed. These media are used to 

 determine the effect of bacteria upon the different sugars. 



(c) Glycerin-peptone Bouillon. After filtration, 3 to 5 per cent, of 

 glycerin is added to the peptone bouillon and the whole again sterilized. 

 This medium is used especially for the growth of the tubercle bacilli. 



(d) Mannite-peptone Bouillon. This is prepared by adding 1 per cent, 

 mannite to the peptone bouillon. It is used especially in differentiating 



Arnold steam sterilizer. 



