214 ELEMENTS OF BOTANY 
Select a few small roundish potatoes with skins entire and boil 
in water for a sufficient time to cook them through. Cut them in 
halves with a knife well scalded or sterilized, i.c., freed from all living 
organisms in a flame, and lay each on a saucer, with cut surface up, 
covering each with a glass tumbler. The tumblers and saucers 
should be well scalded or kept in boiling water for half an hour 
and used without wiping. Sterilization may be improved by baking 
them in an oven for an hour. 
268. Inoculation. — The culture media prepared as above may now 
be inoculated. Uncover them only when necessary and quickly 
replace the cover. Scrape a little material from the teeth, tongue, 
kitchen sink, floor of house or schoolroom, or any other place you 
may desire to investigate. With the point of a knife blade or a 
needle sterilized in a flame, inoculate a particle of the material to be 
cultivated into the surface of one of the potatoes. Several cultures 
may be made in this way and one or more left uninoculated as 
checks. Another may be left uncovered in the air for half an hour. 
Others nay be made with uncovered potatoes. Number each culture 
and keep a numbered record. 
Keep watch of the cultures, looking at them daily or oftener. As 
soon as any change is noticed on the surface of a culture, make a 
descriptive note of it and continue to record the changes which are 
seen. Note the color of the areas of growth, their size, outline, ele- 
vation above the surface, and any indications of wateriness. Any 
growth showing peculiar colors or other characters of special inter- 
est may be inoculated into freshly prepared culture media, using 
any additional precautions that are practicable to guard against 
contamination. 
269. Microscopic Examination. — Examine some of the cultures. 
Place a particle of the growth on a slide, dilute it with a drop of 
clear water, and place a cover-glass over it. Examine with the 
highest obtainable power of the microscope, at least | in. objective. 
Note the forms and movements, also the sizes if practicable, of any 
bacteria that are found. 
