out salt, 2 grammes, and lactose, 20 grammes, and mix with the
emulsion.

3. Wash the mixture into a sterile litre flask with 200 c.c. meat
extract and add 600 c.c. distilled water.

4. Heat in the steamer at 100 deg. C. for thirty minutes, to completely
dissolve the peptone, etc.

5. _Neutralise carefully to litmus paper_ by the successive additions of
small quantities of decinormal soda solution.

6. Replace in the steamer for twenty minutes to precipitate phosphates,
etc.

7. Filter through two thicknesses of Swedish filter paper.

8. Add sterile litmus solution, sufficient to colour the medium a deep
purple.

9. Tube, and sterilise as for bouillon.

~Lactose Litmus Gelatine (Wurtz).~--

1. Prepare nutrient gelatine (_vide_ page 164, sections 1 to 4).

2. Render the reaction of the medium mass -5.

3. Replace in the steamer at 100 deg. C. for twenty minutes.

4. Clarify with egg as for gelatine.

5. Weigh out lactose, 20 grammes (= 2 per cent.), and dissolve it in the
medium.

6. Filter through papier Chardin.

7. Add sufficient sterile litmus solution to colour the medium pale
lavender.

8. Tube, and sterilise as for nutrient gelatine.

~Lactose Litmus Agar (Wurtz).~--

1. Prepare nutrient agar (_vide_ page 167, sections 1 to 4).

2. Render the reaction of the medium mass -5.

3. Replace in the steamer at 100 deg. C. for twenty minutes.

4. Cool to 60 deg. C. and clarify with egg as for nutrient agar.

5. Weigh out lactose, 20 grammes (= 2 per cent.), and dissolve it in the
medium.

6. Filter through papier Chardin, using the hot-water funnel.

7. Add sterile litmus solution, sufficient to colour the medium a pale
lavender.

8. Tube, and sterilise as for nutrient agar.

~Glycerine Potato Bouillon.~--

1. Take 1 kilo of potatoes, wash thoroughly in water, peel, and grate
finely on a bread-grater.

2. Weigh the potato gratings, place them in a 2-litre flask, and add
distilled water in the proportion of 1 c.c. for every gramme weight of
potato. Allow the flask to stand in the ice-chest for twelve hours.

3. Strain the mixture through butter muslin and filter through Swedish
filter paper into a graduated cylinder. Note the amount of the filtrate.

4. Place the filtrate in a flask, add an equal quantity of distilled
water, and heat in the steam steriliser for sixty minutes.

5. Add glycerine, 4 per cent., mix thoroughly, and again filter.

6. Tube and sterilise as for nutr