This section is from the book "A Handbook Of Invalid Cooking", by Mary A. Boland. Also available from Amazon: Handbook of Invalid Cooking.
Sweetbreads are the pancreatic glands of the calf. They are good while the animal lives on milk, but change their nature when it begins to eat grass and hay, and are then no longer useful for food. The gland consists of two parts, the long, slender portion called the " neck" sweetbread, and the round, thick part known as the "heart" sweetbread. These are sometimes sold separately, but they should be together. Among epicures sweetbreads are considered a dainty, and are certainly a most acceptable form of food for the sick.
To Prepare. As soon as sweetbreads come from market, they should be cleaned and parboiled. Cut off any refuse, - such as pipes, fat, and all bruised portions, - and wash them quickly in cold water. Pour into a saucepan some boiling water, salt it, and add a little lemon-juice or vinegar (not more than a teaspoon to a pint of water); boil the sweetbreads in this for fifteen minutes if they are to be creamed, broiled, or baked, or again cooked in any way; but if they are to be served plain with peas, they should remain on twenty-five or thirty minutes. When done, drain off the water and set them aside to cool. Sweetbreads must always be parboiled as soon as possible after being taken from the animal, as they decay quickly. Sweetbreads may be made white by soaking them in cold water for half an hour; the flavor, however, is said to be injured by so doing.
 
Continue to: