WET TEST — Vaginal fluid or stain extract or swab extract or fresh semen, thinned on staying for some time or by addition of 1% HCl, is taken in a drop on a glass slide and covered with a cover slip and examined under a microscope. Spermatozoa, in its appearance described above may be seen, either motile or dead. When fresh, 80% of the spermatozoa are motile. If kept in dry glass container, by 24 hours about 10% will be still motile. Motility is lost in the vaginal canal within some hours. But in the uterine cavity they may survive for 2-3 days. Sperms disintegrate due to decomposition, with separation of the tail at the neck region (junction of head and tail). In old or decomposed stain, sperms may not be recognized by wet microscopic test. Staining test is necessary in such cases.
STAINING AND MICROSCOPIC EXAMINATION OF SEMEN :
The dried stain extract on the glass slide is first stained with a basic stain (methylene blue or haematoxylin) for 20 minutes. Then it is washed and counter-stained with an acid stain, eosin. The tail and the posterior third of the head takes eosin or reddish stain and the anterior two third of the head takes very light or faint, basic or blue stain.
TEST FOR BLOOD GROUP FACTORS IN THE SEMEN:
SECRETORS — About 80% of the world population secrete their blood group specific substances in their body fluids including semen, sputum, urine, sweat, milk, tears etc. The fibres of the stained part of the cloth can be subjected to mixed agglutination test to find out any group specific substance, secreted by the person. This helps in specific identification of the person. The blood of the suspect is examined to know his blood group. The sputum of the suspect is also examined to see whether he is actually a secretor, so that full value can be given on the said grouping test of seminal fluid.
EXAMINATION AND M.L.I. OF SALIVA STAIN:
1. Suspected stain due to saliva can be confirmed by:
a) Presence of buccal squamous cells (microscopic).
b) Detection of presence of amylase. To test for the presence of amylase, the stain extract is treated with starch solution and incubated at 37°C for 1/2 hour. Then a drop of gram’s iodine is added. If the stain was due to saliva, then there will not be any bluish discolouration because, amylase digests the starch partly to dextrine and then to maltose. If the stain is not due to saliva then there will be bluish discoloration on addition of gram’s iodine, after incubation of the extract with starch.
2. From buccal mucosal cells present in saliva, sex can be determined (Barr bodies).
3. Group of the person can be known by mixed agglutination test with the buccal squamous cells or the fibres from the stained part of the cloth.
4. Some poisons are secreted in the sputum.
EXAMINATION OF VAGINAL FLUID:
In addition to detection of 1. semen and 2. blood, 3. group specific substances can also be detected from the vaginal fluid stain, if the person is a secretor. 4. Examination of vaginal epithelial cells is a good way to know the actual sex in gonadal dysgenesis cases. 5. Presence of vaginal epithelium cells on the glans of the penis of the accused supports sexual intercourse. The glans is rubbed with a moist blotter and subjected to the vapour of iodine. The blotter becomes partly brown if vaginal epithelium cells are present because they contain glycogen which turns brown due to iodine. 6. Vaginal stain extract should also be examined for poisons in a suspected case of criminal abortion.
EXAMINATION OF FAECAL STAINS:
Faecal stains can be confirmed by microscopic examination, when vegetable cells and muscle fibres will be seen, if it is a faecal stain. From faecal stains group specific substances can be detected. Tests for faeces are necessary in alleged sodomy cases. Poisons may be detected from stool in poisoning cases.
TESTS FOR URINE — Stain due to urine may be known by using urease test and also testing the stain for different constituents of urine. Examination of urine may give blood group of the person if he is a secretor. Many poisons are excreted through urine and can be detected in the urine.
EXAMINATION OF SKIN — May help to know the sex, group of the person and detection of some poisons.
EXAMINATION OF TOOTH PULP — For sex and blood group.
EXAMINATION OF NAILS AND DANDRUFF — For blood group.
From nails, poisons (heavy metal, like arsenic) can be detected. Debris on the nail beds may show presence of foreign tissue and blood, which may give sex and blood group of the person concerned.