What had the young lady been in the habit of eating and drinking?
They must fetch what had been left over from her meals, he must see and examine everything.

What had she eaten yesterday evening?
Preserves?
Then what sort of sugar was used, and where was the spoon?
He insisted on seeing everything.
"But doctor," whined old Lapussa, "you surely don't mean to say that the child has been poisoned ?" "I do indeed, and with copper oxide too." "How is that possible ?" "Why, simply because some of her food, preserve, for instance, has been allowed to stand too long in a copper or silver vessel and copperas has been developed." The old man did not know enough of chemistry to understand how copperas could be developed from silver, but he was seriously alarmed.
"I hope there's no danger ?" said he.
"It is a good job you sent for me when you did," replied the doctor, "for otherwise she would have been dead before morning.

Copperas is a very dangerous poison, and if it gets into one's food in large quantities there is practically no antidote.

A vigorous constitution, indeed, has a good chance of throwing it off; but, taking into consideration the state of the young lady's nerves and her general debility, I should say that her case was downright dangerous; anyhow she will be ailing for some time." "Oh, doctor, doctor! and we all love Hetty so much, she is the very light of our eyes! I cannot tell you how anxious I am, on her account I should be so glad, doctor, if you could stay with her night and day and never leave the house.

I would richly recompense you." "I will do all I can, though I can't do that, and unless any unforeseen accident arise, I think I can answer for the result.