Medical Jurisprudence And Toxicology

BLOOD STAINS 95

bands may not be visible evidently from the effects of putrefaction. In that
case the stain should be treated with a drop of a ten per cent solution of
potassium cyanide. A cherry red colour will develop due to the conversion
of hsemochromogen into cyanhaemochromogen with its characteristic absorp-
tion bands similar to those of the former but slightly wider and situated
closely at wave lengths 570-550 and 540-527.20

Tl^e^-inllowing procedure21 is recommended for the detection of blood
stains' on rusty weapons and red coloured fabrics : —

A small portion of the blood stain is taken on a glass slide with a ten
per cent solution of caustic potash, a little glucose powder is added and is
covered with a cover slip. The glass slide is then warmed over a small flame,
when the stain assumes a bright red colour and gives the characteristic
haBmochromogen bands. The red dye on fabrics is usually bleached by this
procedure.

The reduction into haemochromogen may also be brought about by the
Takayama reagent as described before or by an alkaline solution consisting
of 4 grammes of sodium hydrosulphite, 10 cc. of potassium hydroxide (10
per cent) and 2 cc. of alcohol, which is said to be cleaner and much more
efficient.

The spectrum of hsemochromogen or of cyanhsemochrornogen is quite
enough for purposes of identification and expression of a definite opinion
about suspected blood stains. It is not necessary to examine any more
spectra of acid or alkaline haematin, hasmatoporphyrin, etc. For practical
purposes one chemical test, viz. the benzidine test, and a confirmatory spectro-
scopic test for haemochromogen or cyanhasmochromogen, are quite sufficient
for a definite opinion, and these are the principal tests usually employed in
the laboratories of the Slate Chemical Examiners. For very old and
scanty stains where there is not sufficient material for repeating the exami-
nations, the Chemical Examiners are required, by the order of the Govern-
ment of India, to forward the stains as they are, to the Imperial Serologist,
Calcutta, for identification of blood and for determination of its origin by
the serological test.

Biological Examination.—This is undertaken for the purpose of deter-
mining whether the blood of a particular stain is derived from a human being,
from a lower mammalian animal or from a bird.

Precipitin Test.-^Jhis test is based on the principle that a foreign protein
or a protein-containing substance, when injected into an animal, produces
antibodies in the blood serum of that animal, which will form a precipitate
when mixed with a solution of that foreign protein. The protein thus intro-
duced is called the antigen and the antibody capable of forming a precipitate
is called precipitin^ Relying on this principle, Uhlenhuth who made several
experiments and devised a method for recognizing the different kinds of
mammalian blood, found that the test was exceedingly delicate and suggested
its applicability for the detection of human blood in medico-legal inquiries.
Other workers have elaborated its technique to its perfection and have given
it the name of the precipitin test.%The method consists in injecting sub-
cutaneously, intraperitoneally or intravenously a rabbit or a fowl with blood
serum of an animal, a man for instance, at regular intervals. After a certain
number of injections the serum obtained from the injected animal, when
sufficiently diluted and added to a clear serum of human blood, produces
at first a turbidity and then a fiocculent precipitate but fails to do so with

20. Greval, Roy Chowdhery and Das found that the absorption band on the longer
wave length side (red end) was intense and that on the shorter wave length side (violet
end) was faint but broader (vide Ind. Jour. Med. Res., Vol. XXXIII, No. 1, May 1945,
p. 173).

21. Madras Chera. Exam. Annual Rep., 1940, p. 10.