CULTIVATION. 145 
albumunious material is filtered off. It must still be slightly alkaline or 
neutral. If, after this, the fluid still remains opaque or cloudy, the 
white of an egg must be added and the whole boiled again for half an 
hour. The egg albumen coagulation carries off with it the slight tur- 
bidity which was present. The clear fluid is again sterilized and 
poured into sterilized tubes, which are kept carefully plugged with 
cotton wool. i 
What is the common way of preparing potato? 
The potato is thoroughly scrubbed and the eyes and discolored por- 
tions are cut out. It is washed in a 1-1000 solution of corrosive sub- 
limate. After being cooked in a steam sterilizer and cut in halves with 
a sterilized knife the pieces are placed in a sterilized covered glass dish, 
having on its bottom a layer of filter paper moistened with a one per 
cent. solution of corrosive sublimate. This moist paper is for the pur- 
pose of keeping the air in the dish in a moist condition. 
Potatoes prepared in this way are inoculated by being rubbed with 
a sterilized platinum wire carrying the bacteria to be grown. 
How are-potatoes prepared to be used in test-tube cultures ? 
They are first scrubbed thoroughly and pared. Then with a hollow 
tin cylinder round plugs of suitable size are cut out of the raw potato. 
These are divided diagonally and placed in the test tubes with the thick 
end down. The tube is then plugged with cotton wool and the whole 
sterilized in a steam sterilizer. The heat of the sterilizing steam cooks 
the potato at the same time. 
In what respect is a solid medium superior to a liquid one ? 
The colonies of bacteria on solid media develop separately and do not 
mix as in fluid media. 
Describe the solid culture medium devised by Koch. 
It is a medium that at one time may be liquefied and at another 
rendered solid, and in either state it is transparent. Beef bouillon 
forms the nutrient portion and gelatin the solidifying material. 
Give the method of preparing it. 
Prepare 1000 grams of meat water as in making beef bouillon, to it 
add 10 grams of peptone, 5 grams of common table salt and 100 grams 
of French gelatin. Shake well in a large flask and heat in a water 
bath for half an hour or until the gelatin is dissolved. It is then 
neutralized by the careful addition of a solution of carbonate of soda. 
To this mixture add the white of an egg dissolved in 25 cc. of water, 
10—H.P.B. 
