22 FIRESIDE SCIENCE. 



influence of animal heat and the vital forces. They 

 embrace a series of decomposing and recomposing 

 operations which it is difficult to imitate in the 

 laboratory. In the experiment to which allusion 

 has been made, the amount of earthy material found 

 in the eggs and the excrement of the hen exceeded 

 that contained in the food she consumed. This 

 seems paradoxical, and can only be explained upon 

 the ground that birds as well as animals have the 

 power, in times of exigency, of drawing upon their 

 own bodies for material which is required to per- 

 form necessary functions. 



The shell of an ordinary sized hen's egg weighs 

 about 106 grains, that is, the inorganic portion of 

 it ; and if a bird lays 100 eggs in a year, she pro- 

 duces about 22 ounces of nearly pure carbonate of 

 lime in that period of time, which would afford 

 chalk enough to meet the wants of a farmer, or 

 perhaps even of a house carpenter of moderate 

 business, for a twelvemonth. 



If a farmer has a flock of one hundred hens, 

 they produce in egg-shells about 137 pounds 

 of chalk annually ; and yet not a pound of the 

 substance, or perhaps not even* an ounce, exists 

 around the farm-house within the circuit of their 

 feeding-ground. This is a source of lime pro- 

 duction not usually recognized by farmers or hen- 

 fanciers, and it is by no means insignificant. The 



