_Salting_ may be done by either the brine or dry method. To prepare a brine bath, add salt to a tank of water until it will float an egg, and add a pailful or more of salt every few days thereafter to keep up the strength. The cheese is then placed in this bath and left for three to five days, depending on the saltiness desired. As the cheese floats with a little of the rind above the surface, it should be turned a few times to insure uniformity of salting. With dry salting, the salt is rubbed on the cheese by hand or with a stiff brush, and any excess carefully wiped off, leaving only a slight sprinkle on the surface to work into the cheese. +271. Curing Swiss.+--From the salting-room, the cheese goes to the first one of two curing-rooms, where the unique process of the development of the characteristic eyes takes place. During the curing period of either round or block Swiss, constant attention must be paid to the cheese. They must be turned every day at first, and then every second or third day toward the end of the curing period. Also, great care must be taken that no mold starts growing, as it will soon work into the cheese, and spoil its flavor. The best way of preventing mold is by washing the cheese, in either clean or slightly salted water, as often as possible. A stiff brush is mostly used for this. The development of the "eyes" or holes is the difficult part of the whole process. It is not known exactly what causes the development, but it is attributed to micro-organisms or enzymes. The gas in these eyes has been examined and found to be carbon dioxide and free nitrogen. Sometimes hydrogen is found. This comes from the original fermentation of the milk-sugar and remains to contaminate the normal eye. The nitrogen[124] is included from the original air. Propionic acid is formed at the same time as the eyes, and they are said to be the result of a propionic ferment of lactic acid. The interior of the cheese is anaërobic, due to low permeability and high oxygen-absorbing quality. This propionic bacterium cannot, however, account for all the carbon dioxide produced. After the eyes have started, their further development depends on temperature and humidity of the air, and on the moisture of the cheese, as regulated by the amount of salt used. The first room has a temperature of 70° F. to start the eyes, which is later lowered in the second curing-room to about 60° to check the development. When any local fermentive action starts, it may be checked by rubbing salt on the affected part. The humidity of the room is very important, because a cheese will quickly dry out in a dry room, due to evaporation from the surface. To prevent this, it is well to spray the floor with water, or to have a steam jet in the room.