1852 The Cornell Reading-Courses 



developing chick by the combining of carbon and oxygen, and this in- 

 creases in amount as the embryo grows. The eggs need, therefore, only 

 ■ a comparatively small amount of air during the first few days of incubation, 

 as only a smaU amount of carbon dioxide is given off during this period. 

 It is asserted by some authorities that the natural amount of carbon 

 dioxide given off by the eggs is beneficial, on the ground that it aids in 

 dissolving the carbonate of lime in the shells. Some experimenters go 

 so far as to assert that it is really necessary for the successful development 

 of the embryos. The writer is not yet ready to indorse this statement. 



Excessive ventilation, permitting a rapid circulation of air in the egg 

 chamber, would result in rapid evaporation of the moisture. Hence, for 

 normal development of the embryos it is necessary to provide moderate, 

 well-controlled ventilation throughout the period of incubation, or to 

 check ventilation during the first part of the period and then to increase 

 it as it becomes necessary. With either method it is essential that mois- 

 ture shall be present in order to prevent undue evaporation. If the 

 ventilation is checked, it is not considered so necessary to supply moisture 

 as it is in cases where ventilation is continued through the entire period 

 of incubation, because evaporation takes place much more slowly when 

 the change of air in the egg chamber is lessened than when it is increased. 

 The amount of evaporation of the egg contents may be controlled very 

 successfully by maintaining a proper degree of humidity in air that is 

 taken into the incubator. The humidity under a sitting hen usually 

 registers about 60 per cent. If a non-moisture incubator is operated 

 in a room in which the air is dry, owing to climatic conditions, or a room 

 in which several incubators are being operated, it may be necessary to 

 supply moisture. 



Supplying moisture. — Unless the manufacturers so direct, moisture 

 should never be suppHed in an incubator.^ If non-moisture incubators 

 are operated in a dry place, the floor of the room may be kept wet unless 

 it is of wood, in which event pans containing water may be placed under 

 the incubators. The amount of moisture exhaled from a surface in 

 a given space of time is governed by the extent of the surface and not 

 by the depth of the receptacle. This principle should be remembered 

 when supplying moisture in a room or in an incubator. In using incu- 

 bators in which arrangements have been made for supplying moisture, 

 certain days should be set for looking after the supply in order to avoid 

 a possible chance of the moisture receptacle's becoming dry. The correct 

 amoimt of moisture to be supplied to a given nimiber of eggs can be 

 determined only by watching and studying the size of the air cells. 



« The same amount of moisture placed above the eggs that is often placed underneath them would cause 

 Stattlfete saturation a-nd wc 

 sM6uia aVways be followed. 



cctottlfe'te satttration a-nd would damage the hatch in most incubators; hence the manufacturers directions 



