There’s a bunch of blood at a potential crime scene. Then it’s found to be pig’s blood.
How long ago would that scenario have been possible? Were there tests for such a thing in the early to mid 20th century?
I suspect the same techniques that allowed doctors to identify human hormones in the 1930s (the “rabbit test”) could identify human blood characteristics and distinguish them from pig blood.
For what it’s worth, in the first Sherlock Holmes story, Holmes makes a big deal out of just being able to tell the difference between blood (species unspecified) and red paint.
The precipitin test was developed in 1901:
IIRC, he’s excited because he found a reagent that reacts with human blood but no other kind of blood. (evidently pre-figuring Mr. Uhlenhuth’s real-world discovery). Obviously very significant for a detective, particularly in an age when more people were involved in killing chickens or other activities that could lead to plausibly claiming a blood stain is not from human blood.
Well, the reagent mentioned in “A Study in Scarlet” was for hemoglobin, (though Doyle seems to have misspelled it even according to the usage at the time!) and he makes no mention of being able to differentiate human blood from animal, just old bloodstains versus red mud/fruit/rust or whatever.
There may well be a different, more specific reagent mentioned in a different book or story. Holmes would certainly have found the distinction between human and animal blood a forensically important one.
Hmm. Evidently, I did Not Recall Correctly.
Unless there’s somewhere else… my memory is Holmes explaining to Watson why a test for specifically human blood would be useful, in case a suspect claims the blood on his sleeve is from an animal. But at this point, I wouldn’t bet too much on my memory, when Google says otherwise.
Pour a bucket of it over an emotionally unstable psychokinetic chick in a prom dress.
If the town is still standing when she calms down, it was probably human blood.