Scientific Aids in Criminal Investigation
| Date | 01 July 1938 |
| Author | F. G. Tryhorn |
| DOI | 10.1177/0032258X3801100303 |
| Published date | 01 July 1938 |
| Subject Matter | Article |
Scientific Aids
in
Criminal
Investigation
By F. G. TRYHORN, D.Sc. (Liv.), A.I.e.
Professor of Chemistry, University College, Hull.
PART
XI
THE
EXAMINATION OF BLOOD AND BLOODSTAINS
(continued)
IN
previous articles (VII and
VIII)
adescription was given
of chemical and spectroscopic tests which may be applied to
determine whether or not a given stain is one of blood.
The
purely chemical tests are indecisive because they are positive
also in the case of many substances other than blood. Positive
reactions to such tests only indicate the possibility that the
stain is blood. Positive results in the spectroscopic examina-
tion of a stain are decisive in the sense that they show that the
stain is one of blood;
but
they do not indicate the origin of the
blood.
The
chemical tests are based on the presence in blood
of substances which are present also in many other natural
products.
The
spectroscopic tests are based on the red
colouring matter (hremoglobin) of blood: this is common to
blood of all animal species, and the test fails therefore to be
distinctive as to the species of the blood.
In
police work the question of the origin, or species, of
the blood is usually of the greatest importance, and therefore
further distinguishing tests are necessary.
Reference has previously been made to the possibility of
determining the species of a blood by a microscopical examina-
tion of its corpuscles.
This
is possible because the red
corpuscles of the blood of different species differ in size, shape,
and structure. Distinction on this basis is possible, however,
only in the case of quite fresh stains, owing to the irreversible
shrinkage of the corpuscles on drying.
282
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