2. Weigh out and mix

Pota.s.sium phosphate 0.10 gramme Sodium carbonate 0.60 gramme

and dissolve in

Distilled water 50 c.c.

Label--Solution B.

3. Weigh out

Silicic acid 3.4 grammes

and dissolve in

Distilled water 100 c.c.

4. Pour the silicic acid solution into a large porcelain basin.

5. Mix equal quant.i.ties of the solutions A and B; then add successive small quant.i.ties of the mixed salts to the silicic acid solution, stirring continuously with a gla.s.s rod, until a jelly of sufficiently firm consistence has been formed.

6. Spread a layer of this jelly over the bottom of each of several large capsules or "plates."

7. Sterilise in the steamer at 100 C. for thirty minutes on each of three consecutive days.

_Media for the Study of Water Bacteria._

~Naehrstoff Agar (Hesse and Niedner).~--(_For enumeration of water organisms._)

1. Weigh out: agar, 12.5 grammes and emulsify in 250 c.c. distilled water.

2. Wash the agar emulsion into a tared 2-litre flask with a further 250 c.c. distilled water.

3. Dissolve by bubbling live steam through the mixture.

4. Emulsify Naehrstoff-Heyden (alb.u.mose) 7.5 grammes in 200 c.c. cold distilled water and add to melted agar.

5. Adjust weight of medium ma.s.s to the calculated figure for one litre (1020 grammes) by addition of distilled water at 100 C.

6. Clarify with white of egg and filter.

7. Tube in quant.i.ties of 10 c.c. and sterilise in the steamer at 100 C.

for twenty minutes on each of three successive days.

~Bile Salt Broth--Double Strength.~--

1. Weigh out Witte's peptone, 40 grammes, and emulsify with 300 c.c.

distilled water previously warmed to 60 C.

2. Wash the peptone emulsion into a litre flask with 600 c.c. distilled water.

3. Weigh out sodium taurocholate, 10 grammes, and glucose, 10 grammes; dissolve in 100 c.c. distilled water and add to the peptone emulsion in the flask.

4. Heat in the steamer at 100 C. for twenty minutes.

5. Filter through Swedish filter paper into a sterile flask.

6. Add sterile neutral litmus solution sufficient to colour the medium to a deep purple.

7. Fill into small Erlenmeyer flasks in quant.i.ties of 25 c.c.

8. Sterilise as for nutrient bouillon.

_Media for the Study of Plant Bacteria._

~Beetroot.~-- } ~Carrot.~-- } are prepared tubes and sterilised in a manner ~Turnip.~-- } precisely similar to that described for potato.

~Parsnip.~-- }

~Hay Infusion.~--

1. Weigh out dried hay, 10 grammes, chop it up into fine particles and place in a flask.

2. Add 1000 c.c. distilled water, heated to 70 C.; close the flask with a solid rubber stopper.

3. Macerate in a water-bath at 60 C. for three hours.

4. Replace the stopper by a cotton-wool plug, and heat in the steamer at 100 C. for one hour.

5. Filter through Swedish filter paper.

6. Tube, and sterilise as for nutrient bouillon.

~Haricot Bouillon.~--(_For cultivation of bacteria from tubercles of Legumes._)

1. Measure out 1000 c.c. distilled water into a 2-litre flask.

2. Weigh out 250 grammes haricot beans and add to the water in the flask.

3. Weigh out 10 grammes sodium chloride and add to the contents of the flask.

4. Add 1 c.c. of a 1 per cent. solution of sodium bicarbonate.