_Cooling the Eggs._ There is a considerable difference in the practice of incubator operators with regard to cooling. No cooling should be done until after the first test. After this some incubator men cool the eggs by dropping the doors of the machine. Others take the trays of eggs out and put them on top of the machine. Cooling is usually done once a day. The amount of cooling which the eggs require seems to vary greatly and here again the judgment of the operator comes into play. About the best general rule which can be given is that the eggs should be cooled until they do not feel warm to the face but they should never be cooled to the extent that they feel cold to the face or hands. The length of time to bring this about varies with the age of the eggs and the temperature of the room. _Moisture._ A good deal of moisture is used in incubating duck eggs. It is usual to begin to spray the eggs with water the next day after testing. However, this may vary anywhere from the sixth to the tenth day. They are sprayed quite thoroughly, some men using water enough so that it runs out of the bottom of the machine. No particular care is taken to see that the water used is warm. Ordinary water just as it comes from the pipes is commonly used and is applied by means of a spray nozzle attached to a hose. However, extremely cold water should not be used for this purpose. This spraying is done once or twice a day as the operator may think necessary until the eggs begin to hatch. In many cases even then if the ducklings seem to be drying too fast after they come out of the shell, or to be having difficulty to get out it is well to open the machines and wet the eggs down thoroughly. _Fertility._ The fertility varies with the season that is, with the weather. At the beginning of the laying season when the weather is cold the fertility usually runs rather low. This is likewise true at the end of the laying season when the heat of summer sets in. During the interval between these two times of low fertility there will usually be one or more periods during which the fertility will go down and then come back again. This seems to occur even though the weather remains about the same and though there is no change in the method of feeding. Fertility may be considered to be good when it runs about 85%. When the fertility is running poor the hatching of the eggs left in the machines after testing will usually be poor also.