Certiorari was granted, 293 U.S. 537, 55 S.Ct. 78, 79 L.Ed. -, to review a decree of the Circuit Court of Appeals for the Eighth Circuit, 70 F.(2d) 564, which reversed the decree of the District Court and held valid, but not infringed, the first claim of the Smith patent, No. 1,262,860, of April 16, 1918, for an improved apparatus and method for the incubation of eggs. The Court of Appeals for the Ninth Circuit held the same claim valid and infringed in Waxham v. Smith, 70 F.(2d) 457, in which case certiorari was also granted, 294 U.S. 20, 55 S.Ct. 277, 79 L.Ed. 733. The question thus presented is one of the scope of the claim.
Only so much of the patent as relates to a method for incubation is now involved. Correct appreciation of the contentions made requires a brief exposition of the well-known phenomena which attend the incubation of eggs under natural conditions.
The period for hatching eggs of the domestic hen is twenty-one days. The eggs are cold at the beginning of the period of incubation, although at that time generation has already progressed slightly. Continuation of this process and successful incubation depend upon the application of heat to the eggs, and the maintenance of their temperature at not less than body heat, about 100 F., and not more than 105 F. Any substantial divergence from this range of temperature results in deterioration or death of the embryo, and consequent failure of the hatching process. If the temperature is maintained within this range, the eggs during the first ten days of the period absorb heat required to generate and maintain the life of the embryo. The eggs are then said to be endothermic or heat absorbing. From the eleventh day until the end of the period the embryo has developed to a point at which the egg generates more heat than is needed to keep the embryo alive. They are then said to be exothermic. From that time on the excess heat is given off to the surrounding air or to objects in contact with the eggs, if at a lower temperature than the eggs.
The development of heat accompanies the oxidation of food elements within the egg, in consequence of which it gives off carbon dioxide during the period of incubation and absorbs oxygen from the external air, both of which pass through the shell of the egg and its lining membrane. During the period of incubation there is also gradual evaporation of moisture from the egg, which tends to reduce its temperature slightly. The best results are obtained if the total evaporation during incubation does not exceed about 15 per cent. Evaporation in excess of that amount affects the embryo adversely; the chick when hatched being undeveloped and lacking normal strength.
Successful artificial incubation therefore involves conformity to three principal requisites: The maintenance of proper temperature during the period of incubation, the prevention of excessive evaporation of moisture, and the supply of an adequate amount of oxygen, which involves also the removal from the incubator of the carbon dioxide which results from oxidation of the contents of the egg.
The artificial incubation of eggs is an ancient art. It appears to have been known to the Egyptians two thousand years ago, and for a comparable period to the Chinese. Until Smith, the patentee, carried on his experiments, the effort had been generally to reproduce as nearly as practicable the natural conditions of incubation. In practice eggs, in relatively small numbers, seldom more than 300, and usually less, were placed, on the same level, in a cabinet with heating means above the eggs, so that the temperature above the eggs was maintained at a higher point, about 103 F., than that below. To secure the requisite exposure of the eggs to the higher temperature, it was necessary, in the course of incubation, to turn the eggs frequently, as is done by the hen in nature. Provision was made for supplying fresh air to the cabinet and for humidifying the air within the cabinet. All incubators were of the still air type; that is to say, the only movement of air within the incubator was that caused by variations of temperature at different points within the cabinet, resulting in some transmission of heat by radiation or convection. The opinion seems to have prevailed that the presence of currents of air either within or surrounding the cabinet was harmful. Successful operation of this method required nice adjustments of the heating means so as to avoid overheating as the eggs passed into the more advanced stages of incubation, reaching their highest temperature about the seventeenth day.