Licence: In copyright
Credit: Practical bacteriology for chemical students / by David Ellis. Source: Wellcome Collection.
110/152 (page 98)
Licence: In copyright
Credit: Practical bacteriology for chemical students / by David Ellis. Source: Wellcome Collection.
![Exercise 79. Total Count of Bacteria when incubated at 370 C. It is useful to know how many of the bacteria are of a kind that grow best at the temperature of the body. Proceed exactly as in Exercise 78 but use nutrient- agar in place of gelntine. Count the colonies after 24 hours and make the calcula- tion in the same way as in the preceding exercise. Exercise 80. To find the number of Bac. coli (and allied forms) present in a sample of Sewage or Sewage-effluent. We may emphasize once more the importance of a thorough knowledge of Bac. coli. The presence of Bac. coli marks the presence of excremental constitutents either by direct or indirect contamination, and the numbers of this organism present in a sample gives the latter at once its biological status, and its potential capacity for undermining the public health. 1. Melt 10 c.c. of nutrient gelatine and pour into a Petri- dish. Allow gelatine to set. 2. Take o*i c.c. from No 3 dilution (see Exercise 77) and pour it on surface of gelatine in Petri-dish, 3. Spread out the liquid over the whole of the surface of the gelatine. [A sterilised Platinum spreader is the best instrument for spreading. If a spreader is not available a small piece of wire can be bent in the form of a triangle and used for the purpose. The apex is held between thumb and forefinger, whilst the base is laid on the gelatine. It is an easy matter to draw the base over the surface of the gelatine and thus spread the liquid.] 4. Incubate at 20 0 C. We have next to recognize the Bac. coli colonies. In this experiment all the colonies will appear on the surface and hence will exhibit their characteristic growths. The student must make himself acquainted with the appearance of Bac. coli surface colonies on gelatine and it would be well to have at hand a Petri-dish o](https://iiif.wellcomecollection.org/image/b29808686_0110.jp2/full/800%2C/0/default.jpg)
