DISINFECTION 347 
Note the gas bubbles rising in the closed arm. Remove a little of the sediment and 
examine under the microscope (both stained and unstained). Note the clusters of 
budding yeast cells. How do they compare with the cells in the yeast cake? After 
the arm is about half-full of gas, test with NaOH as described in No. 19. By the 
amount of gas dissolved by the NaOH determine how much of the gas is COs. 
Does any fermentation occur in the sterilized tubes? In the original unsterilized 
and uninoculated tubes? If fermentation occurs in the latter examine with a micro- 
scope to see if yeast is present. 
No. 37. Decay of Fruit.—Select some sound apples and inoculate them with 
mold spores by dipping the tip of a knife-blade into a mass of mold spores of the 
growths in No 34 and thrusting the tip through the skin of the apple. It will be 
best to inoculate different apples with each of the kinds of mold that have grown 
on the objects in No. 34, some of which will probably be the species to produce decay 
Place the apples in a fruit jar, close the mouth, not too tightly, and set aside in a 
warm place. Examine day by day and note that decay soon begins, starting at the 
inoculated points. Allow the decay to continue till the mold breaks through the 
surface and produces spores. If decay does not occur, it means that the species of 
mold used were not those that produce decay, and the experiment should be re- 
peated with molds from other sources. 
DISINFECTION 
No. 38 Disinfectants—Of the many disinfectants in use three are of particular 
value. These, in the strength commonly used, are the following: 
Carbolie Acid Solution, 1-20 
Carbolic acid crystals, 25 gm. 
Water, 500 C.Cc. 
In weighing the crystals of carbolic care should be taken not to touch them 
with the fingers since they will burn the skin. 
Corrosive Sublimate Solution, 1-1,000 
Corrosive sublimate, I gm. 
Water, I,000 C.c. 
In making and handling these solutions it should be borne in mind that they are 
very poisonous. 
Chlorid of Lime 
Fresh chlorid of lime. 25 gm. 
Water, 500 C.C. 
This disinfectant is cheap and effective if fresh, but it will not keep, and should 
be made up at the time of using. One pound of the chlorid of lime in six gallons of 
water will make up an efficient, cheap disinfectant for disinfecting walls and floors 
of rooms and has the advantage of being non-poisonous. 
