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.

    103/152 (page 91)
    every one or at least the vast majority of the bacteria in the sample to form colonies. It is necessary therefore to give them enough room on the plates to form colonies comfortably. 1. Set 2 sterilised conical flasks (30 to 50 c.c. capacity) on the table. Each should be plugged with cotton wool. 2. Sterilise a number of 1 c.c. pipettes. 3. Add 9 c.c. sterile water to each of the three conical flasks. 4. Lift up 1 c.c. of the water to be examined with a pipette and add to contents of one of the conical flasks (Call this flask No. 1). 5. Lay pipette aside and do not use it again for this ex- periment. 6. Lift up another pipette and after shaking No. 1 flask thoroughly, transfer 1 c c. from it to another conical flask (No. 2). 7. Set 2 sterile Petri-dishes on the table. 8. Melt 2 Nutrient-agar-tubes. 9. Pick up a third pipette, and with it transfer 1 c.c. from No. 1 flask into one of the melted Agar-tubes. 10. Pour contents of the Agar-tube into one of the Petri- dishes. 11. With a fourth pipette, remove 1 c.c. from No 2 flask, pour contents into another of the melted Agar-tubes, then empty contents of Agar-tube into the second Petri-dish. 12. Place both Petri-dishes in Incubator at 28°—320 C. Calculation. Flask No 1 contained . 9 c.c. water To it was added 1 c.c. of sample-water Total = 10 c.c. Hence if we remove x c.c. from this flask this 1 c.c. will contain ^ c.c. of the sample water. When therefore we added 1 c.c. from this flask to the Agar- tube and plated the contents, we really added only , !u th of a c.c. of the sample water, the rest viz. y~ c.c. being