Licence: In copyright
Credit: Practical bacteriology for chemical students / by David Ellis. Source: Wellcome Collection.
117/152 (page 105)
Licence: In copyright
Credit: Practical bacteriology for chemical students / by David Ellis. Source: Wellcome Collection.
![If 110 clotting of the milk and no reddening of the litmus take place with -ooi c.c. of the sample, the absence of B. coli and allies from c.c. of the sample may be inferred. [See preceding exercise for the argument upon which this inference is based]. A negative result with -ooi c.c. of the sample comes within the standard deemed necessary to justify a polluted water being followed to flow into a stream. Exercise 87. To find the number of Bcte. coli and allies by the “Gasv test. 1. Melt a gelatine-tube and pour into it 2 drops of the sample under investigation. 2. Incubate at room-temperature. It has been stated that a water should be ‘passed’ for non-drinking purposes if two drops of it (= *i c.c.) in melted nutrient gelatine does not result in gas formation after incuba- tion. Note, however, that this experiment is not a crucial test and is only useful for purposes of confirmation. Houston’s Provisional Standards. The following standard was provisionally adopted by Dr. Houston in determining whether a polluted water should or should not be allowed to pass into open streams without further treatment. The polluted water was allowed to pass if it conformed to the following. Total no. of bacteria. 1. Gelatine at 200 C. 2. Agar at 37 0 C. 3. Bac. coli. 4. B. enteritidis sporogenes) “Gas” test' J Less 100.000 per c.c. „ 10.000 „ „ „ than 1.000 per c.c. Negative result with O’1 c.c. 5. Indol test 6. Neutral-red broth test Negative result 7. Bile salt broth test with o^ooi c.c. 8. Litmus milk test](https://iiif.wellcomecollection.org/image/b29808686_0117.jp2/full/800%2C/0/default.jpg)
