This is caused by giving unnatural food to the bird, which destroys the
digestive power of its stomach. In this case it disgorges, ruffles its
feathers, and does not arrange them, and becomes thin very fast. The
best thing is to make it swallow a common spider, which purges it, and
put a rusty nail into its water, which strengthens the intestines,
giving it at the same time its proper and natural food. Green food, such
as lettuce, endive, chickweed, and particularly water-cresses, is the
safest remedy. A very great appetite is a sign of this disease. A
siskin, that was dying of atrophy, had nothing but water-cresses for
three days following, and on the fourth he sung.