438 Growth of Chickens in Confinement 
em. of body weight respectively. Chicken 44 @ laid eggs after 
178 days of age. The male bird, No. 57, reached a stage of de- 
velopment at which it crowed like an adult. 
Despite the small proportion of the experimental birds which 
erew as well as did those here pictured, the success already 
achieved in the absence of dietary factors hitherto assumed to be 
essential for the growth of chickens, and also under supposedly 
adverse conditions of housing, encourages us to believe that all of 
the essentials for the nutrition and adequate growth of chickens 
under laboratory conditions can be ascertained, and that these 
will be controllable in much the same way as has proved possible 
in the case of other animals. The question of “roughage,” suit- 
able salts, proteins, and food hormones needs to be approached 
from new angles in the case of species that have characteristics 
of digestion and metabolism and structural requirements some- 
what different from those of most mammals. 
EXPLANATION OF PLATES. 
PLATE 4, 
Figs. 1 and 2. Photographs of Rhode Island Red Chickens 5 f# and6¢ 
(shown at an earlier age in our paper)? at the age of 322 days. They 
weighed between 6 and 7 pounds each. 
~ 
PLATE 5. 
Fies. 8 and 4. White Leghorn Chickens 11 @ and 12 9? raised in the 
laboratory without green food from the age of 3 weeks. The photographs 
show them at an age of 271 days when they weighed 3.3 and 2.5 pounds 
respectively. . 
PLATE 6. 
Fras. 5 and 6. White Leghorn Chickens 44 9 and 57 & raised in the 
laboratory without green food from the time they were a day old. The 
photographs show them at the age of 164 days when they weighed 2.8 
pounds, each. 
