12) 
TWENTY-FIFTH ANNIVERSARY REPORT. 
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During the first period eggs were produced by the hens at the 
rate of one pound for every 3.9 pounds of dry matter in the food, 
and during the second period one pound for every 2.6 pounds. 
The change in live weight during either period was slight, no more 
than might occur at any time within a few minutes. 
The eggs laid during the first period contained calcium equiva- 
lent to 48.43 grams of carbonate of lime, mostly in the shell. The 
ordinary foods and drinking water given them contained calcium 
in different combinations enough to make 7.62 grams of carbonate 
of lime. Of the lime in the eggs over 84 per ct. was unaccounted 
for by any food except the oyster shell taken by the hens, which 
contained 93.8 grams carbonate of lime. 
In the eggs laid during the second period there was found cal- 
cium, mostly in the shell, equivalent to nearly 88 grams carbonate 
of lime, while the food and drinking water contained calcium in 
different combinations equivalent to only about 10 grams of car- 
bonate of lime. Over 88 per ct. of the lime in the eggs was unac- 
counted for except by that in the oyster shell eaten, which contained 
181 grams of carbonate. 
The margin was so great that no other conclusion seemed pos- 
siple except that the egg shells were constructed from material 
derived in large part from the oyster shell. 
In connection with this experiment another feeding trial was 
carried on with a pen of hens under similar conditions except that 
clear glass in small fragments was fed instead of oyster shell. 
Fewer eggs were laid by these hens, and with thinner shells. During 
one period the eggs and shells contained about 1.6 grams and in 
another 1.2 grams more calcium than was found in the food and 
water. The glass eaten contained, in one case twelve and in the 
other thirty times this amount, but it was not considered that any 
of this was available, being combined in the form of various silicates 
unaffected by ordinary solvents. It was thought more probable that 
the small amount was obtained from pebbles of limestone swallowed 
long before, for a few small. rounded fragments of such were found 
in the dung, and these had been subjected to conditions that in the 
one case made oyster. shell available. 
The hens having access to oyster shell took this to the proportion 
of from about 5 to 7 per ct. of the total water-free food while those 
without shell ate glass to the proportion of 30 per ct. of the water- 
free food and would ravenously take very much more if permitted, 
apparently all that could be swallowed. Other hens given glass 
