A REVOLUTION IN EGG PRODUCTION 33 



ing egg will go through, and still produce a healthy chicken, 

 is hard to determine. 



We know that sustained high temperatures are fatal, that 

 sustained low temperatures mean the death of the germ, that 

 lack of moisture drys down the embryo, so that it cannot de- 

 velop properly, and causes it to stick to the shell, thus pre- 

 venting it from freeing itself at the last, and also that an 

 excess of moisture develops the chicken out of proportion, 

 causing it to fill the shell so full that the chicken cannot turn 

 around freely and sufficiently to break its prison walls, when 

 the time of development is up. 



A sitting hen gets off the nest to feed, and sometimes stays 

 off the nest, even in cool temperature for two or three hours, 

 and still brings off a goodly hatch of youngsters. 



A hen also turns her eggs. Whether she knows why she 

 turns them, or not, is a question. Turning the eggs helps to 

 prevent the embryo sticking to the shell, because the construc- 

 tion of the egg always keeps the live germ uppermost, even 

 before incubation starts, and during incubation the growing 

 embryo remains in a suspended condition in the egg, with the 

 development always on the upper side, and if an egg is turned, 

 the contents will shift so as to keep this same uppermost posi- 

 tion, and thus change the position relative to the shell. It is the 

 weakening of these provisions, through staleness of the eggs 

 which causes the "spots" which are thrown out in candling 

 when they reach the market. 



The probabilities are that a hen moves the eggs (turns 

 them) in order to get the cooler outside eggs under her, and 

 thus relieve her feverish condition ; and in endeavoring to 

 increase her own comfort kills two birds with one stone ; first, 

 insures that the eggs are turned, and second, that all the eggs, 

 by being moved and shifted to the center, get an equal share 

 of heat units in the total period of incubation. 



It requires a certain number of heat units to develop a 

 crop of corn, or any other grain, and these units must be sup- 

 plied before a certain limit of low temperature in the season 

 (that is, before frost) prevents further growth. 



A hatching embryo, in the same way, must have a certain 

 number of heat units, and must have them without sustained 

 variation above or below certain limits, and also within a 

 certain time. If the heat is maintained at too low an average 



