When the commercial ferment is received, it should be stored in the refrigerator pending its use so as to retard as much as possible the changes that naturally go on in the culture liquid. Be careful that the bottle is not exposed to the influence of direct sunlight for in a transparent medium the organisms may be readily killed by the disinfecting action of the sun's rays. 2. If a home-made starter is employed, use the greatest possible care in selecting the milk that is to be used as a basis for the starter. 3. For the propagation and perpetuation of the starter from day to day, it is necessary that the same should be grown in milk that is as germ-free as it is possible to secure it. For this purpose sterilize some fresh skim-milk in a covered can that has previously been well steamed. This can be done easily by setting cans containing skim-milk in a vat filled with water and heating the same to 180 deg. F. or above for one-half hour or more. Steam should not be introduced directly. This process destroys all but a few of the most resistant spore-bearing organisms. This will give a cooked flavor to the milk, but will not affect the cream to which the starter is added. Dairy supply houses are now introducing the use of starter cans that are specially made for this purpose. 4. After the heated milk is cooled down to about 70 deg. or 80 deg. F., it can be inoculated with the desired culture. Sometimes it is desirable to "build up" the starter by propagating it first in a smaller volume of milk, and then after this has developed, adding it to a larger amount. This method is of particular value where a large amount of starter is needed for the cream-ripening. 5. After the milk has been inoculated, it should be kept at a temperature that is suitable for the rapid development of the contained bacteria, 65 deg.-75 deg. F., which temperature should be kept as uniform as possible. This can best be done by setting the covered can in a vat filled with warm water. The starter cans are often arranged so that temperature can be controlled by circulating water. 6. The starter should not be too thoroughly curdled when it is needed for use, but should be well soured and only partially curdled for it is difficult to break up thoroughly the curd particles if the starter is completely curdled. If these curd masses are added to ripening cream, white specks may appear in the butter. 7. The vigor of the starter is in all probability stronger when the milk is on the point of curdling than it is after the curd has been formed some time. The continued formation of lactic acid kills many of the bacteria and thus weakens the fermentative action. It is therefore highly important that the acidity of the starter should be closely watched.