_8. The efficiency of home-made refrigerating boxes compared with other means of keeping foods cold._
One box fitted as for fireless cooking, with two or three covered crocks of at least one-half gallon capacity, packed as directed on page 37, with either sawdust, hay, straw, excelsior or paper. Sawdust is specially recommended.
Fill the central crock with a weighed quantity of ice. Fill one or both of the other crocks with water at room temperature. Cover the crocks and close the box. Record the temperature of the water at the end of six, twelve, twenty-four, and forty-eight hours.
Make repeated observations of the temperatures found in ordinary household refrigerators, cellars, cold storage rooms, and any other places used for keeping foods cold. Compare these with the temperatures obtained with a home-made refrigerating box. Is there any economy in using these boxes?
_9. Temperatures which kill disease and putrefactive germs, or check their growth._
It is taken for granted that the student of this subject will be more or less familiar with the nature of bacteria and the elements of bacteriology. It will be recalled that bacteria are a vegetable form of life; that, like all plants, they have, under certain conditions, the power of growth which is shown, largely, by their reproduction; and that under other conditions they are killed. When their growth is merely checked, they are in a dormant state, or perhaps form spores, in either of which cases they are ready to develop as soon as their environment permits. Temperature has much to do with the state of bacteria. If the temperature and other conditions are such that they are in an active or growing state, they will multiply with enormous rapidity. When in food stuffs they effect certain changes by reason of the products which they form as a result of their life processes, or of the alteration in the food materials, owing to their abstraction of some chemical elements or compounds used for their nutrition. When bacteria form unpleasant smelling or tasting substances we speak of them as “putrefactive bacteria.” Those which, if introduced into the bodies of humans or animals, will cause diseases, are called “disease bacteria.” Foods are liable to contain both kinds; and, therefore, it is, obviously, wise to do all that is possible to kill them or prevent their growth.