194 



ARTIFICIAL l.VCUBATIOX. 



eiit pai'ts of its body. Practice, in fine, will promptly teach the best 

 mode of operating. 



It is necessary, as far as possible, to maintain in the apparatus an at- 

 mosphere impregnated with a medium quantity of vapor, and that which 

 is due to the temperature, by keeping vessels filled with water within 

 the hatchers, and especially the stoves. 



According to the observations of several modern philosophers, at 

 the end of fifteen or twenty hours of incubation, and thenceforward to 

 the end of the operation, the chicken respires^ and from the 30th hour 

 it possesses the organs which it is to keep in its adult state. The res- 

 piration takes place by means of the air which is transmitted through 

 the shell, and comes in contact with the vascular membranes of the ani- 

 mal. By obstructing, suspending or vitiating this respiration, the growth 

 of the chicken is .checked, or the difTerent parts of its body are devel- 

 oped in an unequal manner. Hence it is evident that it is necessary to 

 surround the eggs with a pure atmosphere, which must be frequently re- 

 newed, if we would have healthy chickens, or would not see them per- 

 ish in the egg. 



Oviparous animals during incubation, always turn their eggs regular- 

 ly, drawing those at the circumference towards the centre, and the re- 

 verse. This practice should be imitated, and each day the eggs should 

 be turned one-half or one quarter of a revolution, and their places 

 should be changed, that is to say, those which are in the cooler parts 

 should be put in the wanner parts of the instrument, and the reverse. 

 By this manceuvre the respiration of the chicken, which is accomplish- 

 ed at all parts of the shell, takes place in a more perfect manner, and 

 the nutrition being effected uniformly in all parts of the embryo, we have 

 more vigorous and better formed chickens. 



Most of the instruments we have described having regulators of the 

 fire, one or more visits in the twenty-four hours are sufficient, especial- 

 ly in the first stages of incubation. But more attention is required when 

 there are sudden changes in the temperature of the atmosphere, or 

 where, from any cause, we have occasion to change or modify the ope- 

 ration of the heating apparatus, or finally, on the days which precede 

 the hatching, and when it takes place. 



3. The Hatching. The medium period in which chickens hatch 

 is the twenty-hrst day of the incubation ; this term, however, according 

 to the observations of naturalists, may vary considerably, from causes 

 which are mostly unknown, as will be seen from the following table of 

 the extreme and mean terras of the incubation of domestic birds : 



