INCUBATION AND INCUBATORS

—Incubation, originally the sitting of a hen on her eggs, now means the expesure of a living organism to a uniform temperature, under suitable conditions of moisture and ventilation; incubators are enclosed spaces with devices for securing this. For each organism there is a maximum, minimum, and optimum temperature. Incubation should be conducted at the optimum temperature and never reach the maximum or imum. Incubators are employed to hatch, a practice known to the early Chinese and Egyptians. The latter employed Mamals, large closed brick ovens in which you sands of eggs were hatched. These were heated by low _ fires, which, after the twelfth day were allowed to go out. Modern egg incubators are heated by hot air or hot water. The e ential is that the incubator shall maintain a constant temperature, notwithstanding changes in temperature of the outer air, fluctuations in gas pre ure, and the occasional opening of the incubator. After the tenth day the chick, having developed a foetal respiratory organ, produces more heat, and the incubator should automatically adjust itself to this. The providing of increased air for res pir a at i on increases evaporation, and the eggs should be provided with additional moisture. metal cylinders, the space between the walls being packed with non-conducting material. In the centre of the floor there is a box with pipes which, after traversing the incubator, open to the exterior at the top. Inside the box there is a lamp which heats the air, The hot air then circulates through the pipes in the incubator. Fresh air is supplied to the incubator by a tube on either side of the heating box. A jar of water supplies sufficient moisture. The temperature is regulated by a valve over the main pipe from the heating chamber. Increase in temperature opens the valve, decrease closes it. The valve is worked by the expansion of a column of mercury actuating a system of levers. Bacteriological incubators may be hot or cool; the former are kept at 37° C., the latter at 20° ©. Cool incubators are used for gelatin cultures of pathogenic bacteria or to grow non-pathogenic bacteria and moulds. The temperature is maintained in summer by the pa age of cold water round the walls and in winter by warm water. The hot incubators for pathogenic bacteria are square double-walled metal boxes covered with wood. Warm water is poured into the space between the metal walls and heated underneath by oil, gas, or electricity. The flame is regulated by a system of levers which can decrease or increase it when the temperature of the water makes a valve open or shut. The temperature of such an incubator remains constant for months. The air surrounding the incubator should be kept as still as po ible and should be some degrees below the temperature of the incubator. A very carefully regufated and ventilated form of this incubator is used to rear prematurely born infants. _When the child has grown sufficiently the temperature is gradually decreased.