MARKETING EGGS FOR HUMAN FOOD 439 
In order to detect in the general run of eggs those which 
are of poor quality, and the causes, they are subjected to a pro- 
cedure known as candling. Size, cleanliness, and color are appar- 
ent on external inspection; freshness is indicated by firm body; 
A 
Photo by United States Department of Agriculture. : 
Fic. 199.—Stages of development of the embryo during the first week of incubation. 
A, 24 hours; B, 36 hours (see drawing, Fig. 148); C, 72 hours (see drawing, Fig. 149); D, 
7 days; note the very large head with eyes of large proportion (compare Fig. 162). 
and proper care of the egg from the time it was laid can be readily 
determined by holding it before a strong light in such a way 
that the rays of light will shine through the egg and reveal its 
contents to the operator. A candling equipment consists of a 
bright light enclosed in an opaque box or shield, the light for 
testing shining out through a hole in front slightly less in diam- 
