Q: The setting is rural 1925. There are dark stains on trees, shrubs and leaves which my hero believes is blood. My questions are, how would he identify it as blood and how would he discriminate it from animal blood? What tests or experiments that existed in that era could he perform?
Frank James, Ste-Marthe-sur-le-Lac, Canada
A: The two steps needed to distinguish animal blood from human blood are: Determining if the stain or sample is indeed blood and then is it human of animal.
Testing liquids and stains to determine if they are blood is not new. For centuries, the microscope has been used to visually identify blood cells, which would prove that the substance is blood. But this required liquid blood and not the typical crime scene clotted or dried blood, neither of which contain identifiable cells. Several other tests appeared in the 1800s, including the hematin test, developed by Polish scientist Ludwig Teichmann in 1853. This also required liquid blood since in this test the blood was mixed with acetic acid and salt crystals, heated, and then viewed under a microscope. The presence of the characteristic rhomboid crystals proved the sample was blood. This test is similar to the present day Teichmann and Takayama Tests.
The guaiacum test, developed in 1862 by Dutch scientist Izaak Van Deen, used the guaiac resin of a West Indian shrub and is the precursor of the present day phenolphthalein test (see below). In the guaiacum test, the blood sample was mixed with hydrogen peroxide and guaiacum and, if it was indeed blood, a blue color would appear. In 1887, a similar test was used by Sherlock Holmes to identify a bloodstain in the very first Holmes story, A Study in Scarlet.
In 1900, Paul Uhlenhuth developed a serum that reacted only to human blood, and not animal blood. This is an antigen-antibody reaction and is similar to how this testing is done today. The sample would be dissolved in salt water and then the serum would be added. Human blood proteins would then react with the serum, producing complexes that would precipitate (fallout of solution) and darken the serum. Animal blood would cause no such reaction so if a reaction occurred the tester would know that the blood was indeed human and if not it must be animal blood or some other substance. Now we have serums that react with a just about any species of animal you can name and with these lab techs can determine the specific type of animal that shed the blood.
So your character could use guaiacum to determine that the sample was blood and then employ Uhlenhuth’s serum to determine if it was human or not.
The Crime Fiction Writer's Blog 
Frank Karl
April 26, 2012 at 11:00 am
As much as I like a good microchemical test, working with glacial acetic acid under the scope can be “interesting”. Plus you have to have a scope. I’m sure bright field scopes were easy to find in 1925, but I’d suggest the benzidine test. You can run it on filter paper, or perhaps the edge of the newspaper, if you run a blank first.
If it was still wet, perhaps you could make a blood smear and look for characterist 8 um red blood cells.
stay safe……………
Frank
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Gretchen Hayduk-Wroblewski
January 25, 2020 at 2:18 pm
I have a similar question, but the time is 1973. If there was a knife with dried blood on it that contained both human and animal blood, what test would be used to determine that there was human blood on it. Is it possible if after discovering there was human blood, the assumption would be that it was ONLY human blood? In other words, once human blood was detected, would animal blood register alongside it, or would the presence of human blood make the police assume only a person was killed?
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D.P. Lyle, MD
January 25, 2020 at 2:54 pm
It’s easy to determine if the blood was human or animal and to determine the species and testing would also reveal a mixture in most cases. Even if this testing was not done directly the DNA testing would show the mixture also. So yes, they could dop that. Now. But in 1973 there was no DN testing and unless the cops suspected animal blood was involved they might not test for animal blood and would do a simple blood typing which would likely only reveal the type and nothing more. So your sleuth must uncover that an animal might also have been injured and push for animal type testing.
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E. J. Wagner
April 26, 2012 at 12:41 pm
In 1859, von Bunsen,( inventor of the Bunsen burner), developed a method of using spectroscope
attached to a microscope to determine the presence of blood. This worked best with liquid blood, but a skilled practitioner could get good results even from oxidized blood years old.
There’s a more detailed description of this in EJ Wagner’s “The Science of Sherlock Holmes”, pub. Wiley,2007.
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lemitchellrn
April 26, 2012 at 5:38 pm
When was the phenothalein test developed and what is it reacting with?
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D.P. Lyle, MD
April 26, 2012 at 7:30 pm
It tests for hemoglobin in an indirect way thru a type of peroxidase reaction which is too complex to explain but basically it turns pink in the presence of hemoglobin—and a few other things which makes it only a presumptive and not a conclusive test. It is the basis of the Kastle-Meyer test first described in 1903. But this was the first standardized test and the knowledge that phenolphthalein reacted with blood predated that—but I’m not sure by how long. Obviously Conan Doyle was aware of it.
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lemitchellrn
April 27, 2012 at 6:34 am
So, the phenothalein test is really just specific for generic blood, rather than specific for human blood?
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D.P. Lyle, MD
April 27, 2012 at 8:00 am
Generic blood. It is very nonspecific.
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Wally Lind
April 26, 2012 at 10:01 pm
Rural 1925? If there was a detective available he would have been from a state police force, and might have HEARD of this presumptive test. Would he be able to carry it out in the field?
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D.P. Lyle, MD
April 27, 2012 at 7:59 am
In fiction? Yes, of course. That’s what heros do.
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rajshree
August 29, 2012 at 5:29 am
before it ,it is very necessary to find out whether stain found at particular scene of crime is blood or not.
In an attempt to identify blood stains of human origin, DNA was extracted from human and animal dried blood stains and examined using recombinant DNA techniques. As a DNA probe, biotin-labeled or radioisotopically labeled human repetitive sequence 2.3 Kb Hind III fragment (pH 12) in pBR 322 was used. The probe clearly hybridized with human DNA, but not with DNA extracted from frog, fish, mouse, rat, rabbit, chicken, cat, dog, and sheep. DNA from a Japanese monkeies and from a chimpanzee also hybridized with comparable efficiency. The minimum amount of the blood for the species identification was estimated to 0.4 microliter of fresh blood, 2.1 microliters of 2 weeks old blood stain and 3.8 microliters of 3 months old blood stains, indicating that only one drop of human blood is sufficient for species identification. There was no difference of “signal” between isotopic and non-isotopic procedures for DNA analysis. The advantages of the non-isotopic method for species identification of blood stains in forensic science is briefly discussed.
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Dr. Georg Ramsauer
June 1, 2018 at 1:51 am
Paul Uhlenhuth was one of the most famous scientists in the field of criminalistics
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