Organs of Nutrition 137 
where they had become scattered, each group covered 
only a few square yards of ground, and in that space 
lay thickly strewn. . . . The peculiar feature of the 
stones was that they were almost all opaque, white quartz 
pebbles. In one place I found a small group of small 
pebbles of different colour, more like the few brown water- 
worn pebbles which may be picked up hereabouts. These 
lay with a set of bones much smaller than the very large 
bones I found with most of the clusters of pebbles. 
“T did not gather these brown pebbles, as I thought 
it uncertain whether they were gizzard-stones or not, 
though it is possible that the species to which the smaller 
stones belonged was not so careful in selecting white 
stones. 
“A glance at the pebbles lying around in the sur- 
rounding country showed that the quartz-pebbles were 
not collected here. ... Mr. Murdock and I collected 
three sets of pebbles, and these I can pronounce com- 
plete, or nearly so. It is beyond question, too, that each 
set belongs to a distinct bird. No. 1 weighs 3 lb. 9 oz.; 
No. 2 weighs 4 lb.; while No. 3 weighs no less than 5 Ib. 
7 oz.! This giant set contains individual stones weighing 
over 2 o0z.; indeed, I have picked out eight stones weigh- 
ing almost exactly 1 pound.” 
The gizzard of a bird is reflective of its diet, and is 
very quickly affected by any change in the food. For 
example, a captive gull when fed exclusively on fish 
has but little muscular power in the gizzard, but a diet 
of grain will produce a change in that organ, giving it 
grinding power sufficient to crush the kernels of corn. 
