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96                                                MEDICAL  JURISPRUDENCE

the serum of other species) Many workers prefer both intravenous and
intraperitoneal injections of rabbits but the Imperial Serologist with the
Government of India, who examines about 14,000 articles during a year and
has perhaps the largest experience of this kind of work, prefers intravenous
injections of blood serum in fowls except for antiavian serum for which he
employs rabbits. He injects into the wing vein of a fowl 4 cc. on the first
day, 8 cc. on the fourth day and kills the fowl on the twelfth day.jn order
to collect the antiserum.                                                                       w^

The following general remarks on the precipitin sera are quoted from
the annual report of the Imperial Serologist for 1937-38 : 

"(i) Some antisera produced against known sera are sometimes found
unsuitable for the test. They do not yield sharp reactions in the required
dilution and time, that is, they are not sensitive and are, therefore dis-
carded. It may be noted that every individual fowl does not yield a 'suit-
able serum ; some fowls may be entirely refractory and others may produce
only weak sera.

(ii) All antisera should be highly sensitive, reacting with solutions of
animal sera in 1 in 1,000 dilution and reacting with a solution of human
serum in 1 in 40,000 dilution.

(iii) Some antisera react with sera which have not been used for their
production, that is, they are not specific and should, therefore, be discarded
In order to prove their specificity the worker must observe carefully that
they do not react with 1 in 1,000 dilution of sera not used in their production.

(iv) The antisera which give the expected result with a certain dilu-
tion of a known serum (positive control) and do not give unexpected results
with a certain dilution of known sera (negative controls) are only used."

Application of the Precipitin Test. The antisera which differentiate the
blood of closely allied species of animals, e.g. cow's blood from buffalo's or
sheep's blood from goat's are not prepared in the laboratory of the Imperial
Serologist in Calcutta. But the blood of cow and buffalo (taken together)
is differentiated from that of sheep and goat (taken together). This is
carried out by means of two antisera, anti-buffalo and anti-sheep. The
extract from a stain from any of these four animals will react with both the
antisera but much more quickly with the antiserum corresponding to its
group. The results so obtained is confirmed by testing further dilutions of
the extract. A dilution will be found which will react with one of the two
antisera only.22

, A? tjie pecipitin test indicates the presence of the blood protein of an
aSmi ^ a known species its utility has been extended to protein materials
other than blood stains The origin of skin, flesh, bone or even secretions
such as saliva, milk and semen, is established by this test. Small fragments
ot bones and remnants of soft tissues which are scattered deliberately to
conceal ^ cases of murder are sometimes recovered by the police and sent
lor their identification as also for the determination of their source A
historical examination will indicate their nature and a serological exami-
nation will reveal their source provided the fragments of the bones and soft
tissues are not absolutely dry and decomposed.

flp                              em?loyped f detecting the fraudulent  substitution of

flesh of horse  cat  dog, etc   for beef, mutton and pork, and has been lately

tnof wfl          -

tion ot norse tiesh, tor instance, in a sausage.

Technique of the Test.-The first essential thing is to  determine the
presence of blood m a stain before proceeding with the serologicaTtest for

22.   The Imperial Serologists3 Ann. Rep., 1937-38.