PO UL TR T- CRAFT. 1 77 



Don't try to force the temperature up, as it will incline to raise rather than lower, unless 

 the room in which you have the machine is very cold; but on the contrary, if the 

 machine goes up to 103 degrees, and is going over that point, you will have to adjust the 

 regulator a little." (McFetridge). 



256. Ventilation and Moisture. The egg chamber requires to be 

 ventilated, that the gases generated in the eggs may be promptly thrown off. 

 The currents of air created by ventilation may cause a more rapid evaporation 

 of the fluids of the egg than takes place in natural incubation. Some 

 operators use no moisture, some none until the seventeenth or eighteenth day, 

 some a little throughout the hatch. The principle upon which the 

 application of moisture depends is thus lucidly explained by Cyphers : 



" Evaporation from the egg must be held at such a point that the fluids in the 

 embryonic structures are ample to keep the membranes moist up to the time of exclusion, 

 and the rate of evaporation is not the same under any two degrees of temperature. Eggs 

 may be successfully incubated under a temperature that will exclude the chick by the 

 beginning of the nineteenth day, or under one that will not exclude the chick until the 

 twenty-second. The most vigorous chicks will be produced when the eggs are incubated 

 under a temperature that will ripen the embryo by the close of the twentieth day; and any 

 variation from this temperature will proportionately affect the vitality of the chicks and 

 lower the percentage of the hatch. If we have a rate of evaporation to balance the 

 temperature for a twenty-day exclusion, this rate of evaporation will not answer for a 

 nineteen or a twenty-one-day there being too great an amount of evaporation for a 

 nineteen-day, and too little for a twenty-one-day. In neither case will many of the eggs 

 hatch, but if we supply more humidity (the rate of movement of the air remaining the 

 same) for a nineteen-day, and less for a twenty-one-day exclusion, we will have a chance 

 for a fair hatch. If we have a degree of humidity to balance a twenty-day exclusion, and 

 then raise or lower the temperature half a degree, it will injuriously affect the hatch, 

 while a greater variation will ruin it. A constant variation of a degree in temperature 

 will have no injurious effect, but if the temperature is permanently raised or lowered a 

 degree, the atmospheric conditions for a twenty-day exclusion will not answer. 



" It has been universally believed that evaporation from the eggs could only be con- 

 trolled by controlling the humidity of the air in the hatching chamber. The humidity of 

 the air is but one controlling factor, however, as with the same degree of humidity 

 evaporation will be slow or rapid according to the rate of movement of the air, while it 

 is not the same under any two degrees of temperature ; and the constant variation in these 

 two factors is the cause of the extremely varying results. With a due appreciation of 

 these facts, artificial incubation should be more successfully prosecuted in the future than 

 it has been in the past. 



" Evaporation is mainly influenced by the rate of movement of the air within the 

 hatching chamber, and secondarily by the degree of humidity. The rate of movement of 

 the air is controlled by the area and location of the ventilating openings and temperature 

 of the outer atmosphere. The degree of humidity cannot be maintained constant when 

 maintaining a constant movement of the air, and it is not necessary that it should be. 

 The first consideration is to secure a constant rate of movement, and then keep the air 

 from becoming too dry. This is practically all that is necessary in supplying humidity 

 when the rate of movement of the air is maintained constant." 



Cyphers' rules for ventilating, applying specially to bottom ventilation, will 

 not be given here. His method is to adjust the ventilation to keep the air 



