1923] Proceedings of the Academy of Science 13 



trol. Humidity is important throughout the whole of the incubating 

 period and, if not supplied in sufficient amounts when the ventilation 

 requirement is high, the chick will not grow in size or strength enough 

 to free himself from the tough membrane surrounding him or from the 

 shell. If too much moisture be supplied the reverse will occur ; namely, 

 the chick will grow too large to perform the necessary revolution in 

 the shell and the liquids and membrane surrounding him will not 

 have dried enough before the shell is punctured to prevent strangu- 

 lation or gumming up of the bill of the chick in its effort to get out. 



The control of ventilation necessary for the best hatching has 

 been studied from data gained by analysis of the carbon-dioxide 

 found under sitting hens. The curve plotted from the amount of COo 

 per ten thousand parts of air taken each day throughout the period 

 of incubation shows a rapid ascent beginning about the tenth day 

 and amounting to 60 parts in ten thousand at the end of the hatch. 

 The author undertook to devise automatic means for supplying ven- 

 tilation in an amount proportional to the amount of COo found at any 

 time. 



The method of doing this was suggested by the fact that the curve 

 mentioned had been found to be parallel to the curve for the weight 

 of the embryo and also the amount of animal heat generated. On the 

 basis of this proportionality of animal heat, the principle of action de- 

 vised was to have the heat supplied to a horizontal surface above the 

 eggs when heat only was desired, but, when heat and ventilation were 

 desired, have the heat supplied to a vertical flue somewhat longer than 

 the depth of the incubator. All that is necessary to control the 

 amount of ventilation with this arrangement is to adjust at the be- 

 ginning the amount of heat supplied by a rheostat, if electrically oper- 

 ated, or turn up the lamp, if by combustion, so that the amount of 

 heat supplied when the horizontal element is operating is sufficient or 

 slightly too great without the addition of animal heat. As the amount 

 of heat supplied when the vertical heat element is operating is made 

 slightly too small even when the animal heat is at a maximum, the 

 switching of the heat from one element to the other by a thermostat 

 placed just above the eggs gives the required heat control. 



The practical construction of such devices is very simple and 

 their operation very successful. In practice it will be found that the 

 thermostat will operate in the following manner: At the beginning 

 when adjusted the heat will be supplied some nine-tenths of the time 



