INCUBATION OF THE EGG OF THE COMMON FOWL. 373 



But when a perfect ventilation has been obtained, it has pro- 

 duced certain deleterious effects which must be corrected. It is 

 commonplace to say that when evaportion goes on in still air, 

 this air soon becomes saturated, and evaporation, if not stopped, 

 goes on very slowly. If, however, the saturated air is constantly 

 removed and dry air takes its place, the rate of evaporation is 

 increased. It is thus evident that any discussion of ventilation 

 must take into consideration the question of moisture. 



VII. MOISTURE OF EGGS. 



There is probably no one factor so little understood as that of 

 moisture. The most careful observations of the nesting habits 

 of the hen seem to only complicate the matter. A hen may 

 build her nest on the ground, or in the hay loft, and in each case 

 hatch about the same percentage. These facts, which are a mat- 

 ter of every-day observation, lead us to believe that eggs hatch 

 equally well under these variable conditions. The moisture 

 necessary for development must then be controlled by the hen, 

 or egg, or both. 



There are certain constant factors in the production of moisture 

 which we may accept as existing. First of all, the temperature 

 of the air in the nest is far higher than that of the outside air. 

 As the two come in contact, there is more or less moisture pro- 

 duced. A second source is from the perspiration of the skin. 

 A third source is from the egg itself. These three sources sup- 

 ply, so far as we are able to determine, the moisture necessary 

 for the normal development of the egg. 



It is known through the experiment of Reaumer, that exces- 

 sive moisture gives rise to the pathological forms. Dareste 

 (p. 159^ also records an experiment in which the atmosphere 

 was saturated and as a result the albumen liquified and leaked 

 through the shell. Furthermore, Dareste, stated that excessive 

 moisture facilitates the growth of parasitic forms which develop 

 in the albumen. 



The writer made a series of daily hygrometer tests with a 

 view of ascertaining just how much moisture existed in the 

 nests. In testing with the hygrometer, it was placed in the nest 

 among the eggs, and at the end of fifteen minutes was taken out 



