If you should carry that paragraph up to the Supreme Court of the United States in order to find out for good and all whether the fatal casualty happened to the dead man--as the paragraph almost asserts--or to some person or persons not even hinted at in the paragraph, the Supreme Court would be obliged to say that the evidence established nothing with certainty except that there had been a casualty--victim not known.
The context thinks it explains who the victim was, but it does nothing of the kind.

It furnishes some guessing-material of a sort which enables you to infer that it was "we" that suffered the mentioned injury, but if you should carry the language to a court you would not be able to prove that it necessarily meant that.

"We" are Mrs.Eddy; a funny little affectation.

She replaced it later with the more dignified third person.
The quoted paragraph is from Mrs.Eddy's preface to the first revision of Science and Health (1883).

Sixty-four pages further along--in the body of the book (the elephant-range), she went out with that same flint-lock and got this following result.