Practical bacteriology for chemical students / by David Ellis.

  • David Ellis
Date:
1923
Catalogue details

Licence: In copyright

Credit: Practical bacteriology for chemical students / by David Ellis. Source: Wellcome Collection.

    111/152 (page 99)
    containing surface colonies on gelatine of this organism for purposes of comparison. All colonies resembling Bac. coli in their manner of growth should be sub- cultured. These are smooth, thin surface growths, not corrugated. With practice they are easily distinguish- able from most of the others. 5. Make the following cultivations from each colony of this kind. A. Lactose-broth B. Glucose-broth C. Litmus-milk. (See Exercise 66.) D. Gelatine-Shake Culture. (See Exercise 13.) 6. Test further for E. Indol formation. 7. Verify the fact that the eolomes are made up of rod-cells and that these cells are Gram negative. Bac. coli produces both gas and acidity in lactose- and glucose-broth; in the litmus-milk culture the litmus is turned red and the milk coagulated: gas develops in the gelatine shake but no liquefaction takes place. Suppose we find 4 Colonies of this kind. Then -i c.c. of No. 3 dilution contains 4 Bac. coli. Hence 1 c.c. of No. 3 dilution contains 40 Bac. coli. Now 1 c.c. of No. 3 dilution = TT)V^ c.c. of Sample. Hence 1 c.c. of Sample contains 40.000 Bac. coli. Exercise 81. To test a Sewage or Sewage-effluent for Indol- forniing bacteria. (See Exercises 43 and 44.) Indol-forming bacteria are absent as a general rule from pure waters and virgin soils, and abundant in such places when they become contaminated with excremental matter. A negative result is of more value than one that is positive as whilst a negative result shows the absence of B. coli and its adies (which all produce Indol) a positive result does not necessarily indicate the presence of B. coli (or its allies) for ether bacteria also produce Indol. According to many, however, quite apart from the evidence that is afforded of the presence or absence of B. \ 1 (See Exercises 39 — 4