Forensic Hair Studio

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1. Introduction

2. Morphology

3. Importance of hair as evidence

4. Features Hair by analysis

5. Hair down, torn or cut

6. Hair Disorders

7. Hair analysis by neutron reactivation

8. Bibliography

1. Introduction

The evolutionary history of hair is a real puzzle. Whatever its origin, it is clear that mammals owe much of their evolutionary success of this coverage properties hairy. Paradoxically, the migration of humans from their ancestral savannah to populate the earth is related to reversion toward nudity and still maintaining their body temperature.

For evolutionary reasons, hair follicles are not all governed by the same mechanisms of control. As with the hair of animals, seasonal changes in temperature or cause the fall and subsequent replacement of the hair. This process seemed to follow at their own pace, as amended by circulating hormones such as steroids or thyroxine, whose secretion is in turn controlled by the hypothalamus and pituitary. In a subtle way, these mechanisms are still important for homo sapiens.

Development and distribution of hair follicles.

Follicles are inclined (not vertical) in the dermis and the longest extending to the subcutaneous fat layer. An oblique part of the middle area of the follicle wall and extends to the junction between the dermis and the epidermis. Above the muscle, we found one or more sebaceous glands. This area is considered the site of generation of new hair begins and where each new growth cycle.

The core of the hair follicles is listed first in the region of the eyebrows and upper lip, after nine weeks of embryonic development and in other regions, in the fourth week. At 22 weeks, all follicles are established. As the body size increases, the density decreases follicles. It is accepted that typically can not originate new follicles in the skin of adults. All the follicles in an adult man is estimated at 5,000,000, 1,000,000 which is in the head and only in the scalp 100,000. Apparently, there would be substantial differences based on sex or race.

On the scalp, it shows a significant thinning of the hair follicles with aging. Adults 20-30 years of age have an average of 615 per cm2, between 30-50 years of age, the density drops to 485 per cm2, and between 80-90 years is only 435 per cm2. Undoubtedly, we will find a lower density in those affected by alopecia (hair loss). In these cases, recent studies suggest very low densities: women, 260 per cm2; men, 250 per cm2.

Hair: tapered filaments are being developed in the epidermis, its length ranges from several millimeters up to one meter, and the thickness between 0.05 mm and 0.6 mm. Dispense with variable density over the entire skin except the soles of the feet, palms of hands, bottom and side faces of the fingers and toes, the top side of the coffin bone, lips, the glans penis, the foreskin and the inner surface of the labia.

Each hair is formed by a tubular invagination of the skin, the hair follicle whose walls are formed by epidermis and dermis. At the deep end of the hair follicle is a projection of connective tissue papilla constitutes pilosa. The continuous root hair shaft whose diameter is larger and hits the skin.

Connected to each hair, or else there is a gland, sebaceous, are located on the obtuse angle and open at the neck of the follicle.

The first to appear is hair “lanugo”, this hair is lost in the seventh or eighth month of life intra – uterine floating in the amniotic fluid.

In the newborn human being lacks hair marrow and has a length of about 20 to 25 mm, this hair is lost within the first six months being replaced by child hair. The newborn’s hair has its origin in the fourth month of pregnancy piercing the scalp in the sixth month.

At puberty, pubertal hair appears to form the pubic hair, axial and chin, which are usually curly. Instead mentalis hairs are characterized by dryness, axial hair is thinner than previous variable length and can reach several centimeters.

In the nostrils and driver aids can be very long hairs, but as tough as the beard.

Hair is composed of 28% protein, 2% lipids and small amounts of hydrophilic substances, mineral salts and about 70% water.

The hair supporting substance is keratin which is formed by macro molecules consisting of long chains of amino acids joined together.


While touring the new hair is the hair, its cells are queratinizando to enable it to cope with a life of sufficient strength to weather exposure. Full of vigor, strongly pushes his hair out predecessor.

2. Morphology

In the structure of the hair can tell that its axis is composed of outside in, by three planes: the cuticle or flakes, rind or cortex and medulla.

The cuticle: He is credited with strength and stability, is formed by overlapping scales that always point toward the tip of the hair. The scales are formed by specialized cells, which apiulan from the follicle and the hairline, are 6-8 layers.

Methods for studying the cuticle:

It can be seen adding a drop of water, too, after bleaching can be stained with methylene blue and the other method is to make a mold surface. This can be done quickly by hair embedded on a flexible medium such as nail enamel, vinyl or plexiglass solution in chloroform. When the medium has hardened, the hair is removed and remain a clear and distinctive imprint of the hair cuticle, ideal for examination under a compound microscope.

In man, the cuticle is soft and not very prominent, with imbricated scales, in animals, are thick and slightly overlapping.

Generally the hair of the same person, throw squamous index values very similar, and while there are a variety of these indices for different individuals. It is useful in some cases to rule out a hair from another source that is studied.

Its determination is usually performed under microscopic observation using micrometric eyepiece and objective 10 x 25 x.

Bark: It is held of the protective layer of the cuticle, its elements are cortical cells in needle forms, which in regular training aligned in parallel to the length of the hair. They differ in the cortex two main structures semicrystalline One is formed by polypeptide chains in the directions of the hair shaft. These chains are called microfibrils.

Surrounding these fibrils is a structure with high sulfur matrix and proline call.

Most forensic significance stems from the fact crust which is implanted with granules originating pigmented hair color. The color and distribution of these granules give the criminalist important points of comparison between human hair.

The bark is examined microscopically, after the hair has been subjected to a liquid called Canada balsam.

Structural subunits

1. Clockwise alpha helix 2. S-low 3. S-High, 4. Left spiral cord 5. Matrix 6. microfibrils; 7. Macrofibrilla.

Marrow: The central channel running through the hair, in many animals this channel is dominant, occupying most of the hair diameter. The marrow cells are separated by an air network variable appearance, depending on the species.

Not all hairs have medulla, and when they do, vary the degree of medulacin. The bone offers a range of data, it being necessary to consider the extent of the overall diameter and the diameter core.

In man’s hair are averages of index values of from 0.25 to 0.35 medullary and in women less than 0.20.

Human hair may not display or keep it fragmented bone, rarely shows a continuous medulacin, whereas in animals have medulas that are continuous or interrupted.

3. Importance of hair as evidence

Hair is considered an important clue in a variety of crimes. The skills of hairs are very important, even though researchers have not made fully aware of this. The search is also important. The hair can be found on the victim’s clothes in it, under fingernails, between the fingers, linens, combs, brushes. Etc.

Handling of the hair:

Waldeyer, aptly observed: “The dirt adhering to the hair is often more important than the hair.”

Therefore, when you find a hair, you should not take it between your fingers, use a lens helps in many cases to determine the direction of the tip and root of the hair.

Gross, recommended that the hair should be placed on paper and stickers attached by two strips and the ends marked with the letter “a” to the root and the letter “b” for the tip.

In countries where there is a mixed population, this is difficult, because all the hair can not be mounted on a sheet of paper, as the mulatto would rarely, that type of hair preserved in white paper or small paper bags or polyethylene.

Examination of the hair in criminology:

It is recommended to keep the hair in bottles with frosted glass cover, not to alter its characteristic odor. It is best to find hair look. You should take the specimen with forceps and place objects on a slide, cover with a cover slip and examined under a microscope. Then without making a clean copy, add distilled water and examine it carefully. This procedure often discover blood stains, semen, pus etc. After checking this preliminary observation, we proceed to clean the hair.

Cleaning and removal of foreign particles:

To wash the soap solution is used hairs or 10% potassium carbonate interchangeably, then dehydrated with alcohol, passes through xylol and observed with a microscope in aqueous or glycerine can be employed in Canada balsam.

If it is too dark, can be used one of the following solutions peroxide, hot perhydrol, acetic acid, sodium hypochlorite solution, chlorine or alcoholic solution of nitric acid. Good results are obtained with hydrogen peroxide 100 vol. Sodium hydroxide solution combined action. In general hair bleaching is accomplished in approximately 15 minutes, without altering the structure of the specimens.

Aspects expert:

The issues presented expert with the hair or hairs, are:

* Specific Diagnosis.

* Place the body from whom.

* If the hair is cut or torn or fallen.

* Age of the subject.

* Sex.

* If you are from a living or dead.

* Determine if they are stained or discolored.

* Race.

* If the hair corresponds to an individual of a certain profession.

* Hair Trauma.

* The distance from which the fatal shot was fired, in cases of death by firearm.

* The possible existence of poison in the subject from whom.

* The index study flaky hair.

* The blood type of the individual from which it came.

* If you are a healthy hair or have a disease that allows typing.

* Contents of trace metal inorganic elements.

* Perform serological tests that allow for individualized izoencimas fenotipar hair in the studio.

Different characteristics of Hairs

* The nose hair serve as filter of germs and dirt, and that they are located in the hole where the air enters.

* The hair of the armpits and pubic maintain the temperature.

* The body hairs are used to maintain body temperature.

Differences between human hair and animal hair

Human hair and animal hair

4. Hair characteristics according to their analysis

When hair is properly removed from the scene, and referral to the laboratory is accompanied by an adequate number of controls can provide a source corroborating evidence to place an individual at the crime scene. Taking our place is fundamental to an individual at the crime scene and to validate the analysis information are made. It can be useful to reconstruct a criminal, to rule out a suspect, whether the victim fought back and according to some authors, thanks to modern techniques, serve as a personal identification.

The analysis can be derived, from which comes the hair region for this is taken into account the length, diameter, shape of the tip, the material covering the surface and the cross-sectional shape. The beard hairs are more blocked than the skull, showing the effect of shaving with tenure to finish on top. The hairs of the eyebrows, eyelids, nose and ears, are thicker than the hairs of the skull, but many shorter and ending in a point well marked. In the armpit hairs and public regions are observed and inequality longer visible medullary canals eccentrically in a section taken transversely. The hair in this region tends to curl. Trunk and extremities hairs vary in thickness and have less pigment than others.

A coated hair greasy substances undoubtedly comes from the armpit, one curly and vaginal discharge comes from the region published.


The sex determination methods are based on the differential staining of the sex chromosomes. These are

interfaces in the cell nuclei of root sheath of hair.

In the normal female sex chromosomes appear as a homologous pair of X chromosomes

At the interface of the core, one of the X chromosomes appear condensed and can be dyed to appear as a marginal body in it. This body is called marginal Barr body.

In women with XXX chromosomes some of the cores show two Barr bodies, and in case of males with XXY chromosomes, have a single Barr body.

The average man has an X chromosome and one Y Y chromosomes have an affinity to fluoresce with dequinacrina hydrochloride, which does not occur with the chromosome X.

Barr body detection.

This method is practiced by making a smear with the hair root on a glass slide and subsequently tiiendolo orcein in acetic medium.



Stock Solution:

1g of synthetic orcein, 45 ml glacial acetic acid, heat, cool and filter; Dilute 10 ml of the stock solution with 12 ml of distilled water. This solution requires periodic leaks.

Interpretation of results:

If 30% of cells containing Barr bodies, it is considered that the hair is of female origin. If, however not observed Barr corpuscles, cells studied were reported as male origin, it is advisable to determine the Y chromosome, as confirmation.

Detection of Y Chromosome

This method is developed to meet the need to quickly and efficiently the sex of athletes participating in international competition. In the event of having a Y (male) chromosome found an X (female) shows a fluorescent green march near the periphery of cell nuclei.

Subsequently published new techniques to detect the Y chromosome staining based on the same, using the fluorescent dye solution quinacrine hydrochloride.

The following method is designed for the determination of sex in marches dry, and adapted to the hair root sheath.


Mclaive buffer pH 4.6, citric acid, distilled water, sodium phosphate, Store at 4 C.

2 staining solution quinacrine hydrochloride 1% Buffered.

Age of the subject from whom:

Fatal hairs exhibit the characteristics of the hair, absence of medullary canal and pigments contained in the extreme tip. Its thickness ranges from 20 to 50 microns in the fetus to term.

In children aged one month old newborn hair seen in the existence of medullary canal, this fact is a sign of maturity of newborns. The development of the spinal canal, begins soon on the tabs in the remaining hairs.

Esterlen assigns the following values to the average diameter according to age:

12 days 24 micrometers …………………………

6 days ………………………… 37 microns

18 days 38 micrometers …………………………

25 days 55 microns …………………………

15 years ……………………. From 50 to 70 micrometers

Adult (female) ……………… From 80 to 90 micrometers

Adult (man) …………. 80 to 100 micrometers

In elderly hairs tend to decrease in number, thickness, diameter descends through the hair 80 to 60 to 65 microns.

The presence of pigments show that the hairs belong to a subject begins to turn gray, a phenomenon which occurs very different ages.

Dyed or bleached hair:

Hairs one color dyed contrary to natural color; also is dyed in the part near the root.

Considering an isolated dyed hair, it can be said that its color is regular and uniform, however this phenomenon can not be observed in an undyed hair natural.

In dyed hair often lack the brightness and have a crisp look.

Hydrogen peroxide bleaching is the most used. Among the organic dyes, is the most toxic finelendiamina. Causative agent is a lesson in dermatitis.

The problems of identifying the nature of the coloring substance is large, Wood’s light, is an assistant for identifying value bleached hair and dyed. It is very important to compare the color of the hair with hair from another part of the body and also to examine the color of the scalp, which can be stained with dye, used under light wood, dyed hair appears dull and looking tow, the color and fluorescence changes in appearance expert help. The dyes can be recognized by the corresponding analytical techniques.

To determine if a hair has been bleached or not, is subjected to the test of infiltration or impregnation of certain dyes. The natural hair or oxidants, are impregnated easily.

The hair that had been bleached with hydrogen peroxide take a blue color, while natural dyes and treated with non-oxidizing, indifferent to treatment.

Determination of the race:

The scalp hairs provide the safest approach to identify the race, is also very important the presence of bone in them as this plays an important role in determining race.

Microscopically, one can distinguish between white and Caucasian, black, yellow or brown, like the American Indians, Chinese and other Asians.

The technique consists in making a hair inclusion in paraffin or polyester resin and then making transverse cuts with the aid of a microtome.

Among whites, loa scalp hairs differ in texture, shape and degree of pigmentation. The straight hair regularly have a smooth gauge, which decreases gradually from near the tip. Other hairs can be curled or crimped, showing a gradual increase of the undulation, and its diameter decreases alternately along its length, and spinal interrupted type may be slightly eccentric. In both types the pigment varies in intensity, but is concentrated in the peripheral portions of the cortex. In most cases, the pigmented granules are dark and the amount of such granules determines its color to the naked eye, either yellow, red or dark.

American Indians, the Chinese and other Asians generally have straight hair, rustic black, with long stems very pigmented. Cross sections showing cylindrical stems or triangular bone located centrally.

The hair of the black race, is usually curled, twisted and black, varying their size along its entire length as the diameter increases and decreases alternately. A large amount of pigment is in the crust, giving a deep black opaque. The hair, in cross section is oval and may be narrow or almost flat, the medullary canal is situated eccentrically.

The methodology for measuring cross sections of hair, is to take the hair closest to the head and embed in Epon Plastic, plastic tablet obtained with hairs included, is divided into parts with a microtome into 3 microns . The resulting disc is mounted on a glass slide and examined to increase, using a previously calibrated ocular micrometer micron Plantina using micrometer. This allows to measure the major and minor diameters and calculate the cross-sectional area and an index thereof, useful in comparing different hair. The index is defined as the ratio between the smallest diameter and the largest diameter multiplied by 100.

Minor diameter

Index = ——————– x 100

Diameter greater

The cross-sections are calculated by using the formula for the area of an ellipse.

Area = diameter x diameter increased less.

————————————————– – xa


So, that, by a proper use of the values obtained from the index and cross-sectional area, together with the data that shed morphological studies, it is possible to distinguish in a considerable number of cases the individual’s race from which the study hair.

Blood typing:

The techniques produce reliable results in finding the group responsible agglutinogens are:

Absorption elution:

It consists of 6 cm hair cut studio into three equal pieces, after being washed with soap and ether, each piece is allowed 3 hours. with their corresponding antisera (anti-A, anti-B and anti-H), 128 degrees, 64 and 32 respectively with constant agitation, absorption step. Then the pieces were washed with saline hair, are added 0.2% suspensions of red cell corresponding to antisera initially placed. Pieces are subjected to contact hair RBCs at a temperature of 50 C. During 10 minutes and complete the elution step with the aid of ultrasonic vibrations. Finally centrifuged at 120 G. For 2 minutes and observed for agglutination formed.


Radioactive labeled antibody:

The determination method of radioactive labeled antibodies used, and Baetlher described by Kay, 1973, is based on antigen – antibody reaction and can be summarized as follows; the anti A and anti B and anti-H are labeled with iodine 131 and are placed in contact with three pieces of hair previously crushed with a press. Each antibody, with his hair piece, is incubated for a time and then, each slice is exposed to a radiographic film film. When the film reveals, the piece of hair that veiled the plate indicate that the corresponding antigen gave the antigen – antibody and evidence may at hair blood group under study.

5. Hair down, torn or cut:

The freshly cut hair, showing the severed end more or less with clean edges, net, formed acute angles as the edge of the cutting tool.

After 3 days, the tip of the hair cut convexly rounded starts due to growth and the different substances.

The hair that falls naturally shows a filled bulb, full, well-formed, which means that it has reached its full growth.

But those with a hollow bulb or excavated, for not having reached its full development, indicate that were uprooted.

When the fact was very violent to be found in the root there are particles or hanging skin cells adjacent to it.

The hair is virtually indestructible, unless it burn or concerned with acids. It is very important to know the temperature at which burn the hair, it was determined that 100 C, the hair is shortened and loses weight at 150 C, gas bubbles present in the marrow, and 300 C, carbonized. These data are useful to determine at what temperature the body has been exposed to the victim. The heat causes hair microanatomical alterations, indicating these if the hair was subjected to flame or radiant heat.

The hairs begin to suffer alterations in the microstructure at 140 to 150 C, at this temperature the air bubbles in the medullary substance, enlarge and burst, sensing the resistance of the cuticle. For others this phenomenon occurs at 200 C. At 260 C carbonization begins, which is complete at 300 to 400 C

6. Hair Disorders

Trichorrhexis nodosa (Trichorrehexis nodosa)

This condition results in the occurrence of nodular swelling along the stem of which is that it has a tendency to break, especially at the site of the swelling. In this case there are several grayish white nodules in particular on the third end of hair (fig. 22 and 23). This becomes very dry, dry and brittle and breaks at the node. If no fracture cuts through the node, it’s like 2 brushes were in contact (Fig. 24 and 25).

Some authors have attributed the disease to a biochemical defect arginiosuccinico acid metabolism and adopted the idea that trauma can contribute to the formation of a gnarled trichorrhexis.


A hair affected by this disease presents a longitudinal swelling due to abnormal dryness it does at its distal branch or stem quite advanced. There may be multiple branches at the tip of the hair or may be a single branch or bifurcation in several places along the stem.


The hair affected by this disease and they get tangled knots. This kind of disease is due to physical and mechanical forces produced by the reaction of the comb, brush or fingers that some people have a habit to stop by the hair. For McCarthy, burns and washing soaps made with too much detergent, also contribute to cause this disease.

Baynet hair:

This disease is characterized by a widening of the spindle-shaped hair from 2 to 3 mm long, very near the tip. The affected part is darker than the rest of the hair.


Hairs patients have elliptical knots separated by short and tight spaces. It affected the entire hair from root to tip. The knots are generally twice as long as the internodal spaces. The nodes are formed from a thick cuticle wrapping and thin cortical nucleus. The Monilethrix is always inherited.

Abnormalities in case of alopecia:

In this case there is a fall partial or generalized hairs. Can distinguish three forms of hair stunted dead:

Hair obsolete:

The root of a hair seems this condition is intact when started and hair always has a normal length. The root and the stem located immediately below are clearly atrophied.

Hair in exclamation points:

At one point the hair affected by this type of atrophy, it forms a knot or widening due to the dissociation of cortical cells at this location. It follows a loss of cell cohesion and hair in horizontal cracks, broken ends up in places that have been weakened.

Thus, the hair affected by such anomalies have characteristics that indicate a disturbance pigmentari function, a tendency to swell, to dissociate and finally to break in one or more points.

Hair corpses:

In this case, the roots and the hair bulbs are usually thin and bendable as threads at its lower end. Some may have trixorrexis on top.

Abnormalities that take the form of a generalized dystrophy affecting all body pigmentations:

Hair in torsion:

Torsion takes place in the longitudinal direction of the hair shaft and observed at regular intervals, producing tapered portions alternating dark and clear tapered portions, having some analogy with what is seen in the monilethrix.

Ringed Hair:

Hair that has this condition shows light and dark areas. It seems then formed of alternating narrow bands, almost rings, and some other white pigment. The width of these bands varies cases. The parties banded owe their origin to a modification of cortical wrapper and not a modification or a swelling of the bone.

The stone:

Osorio was the first to discover this disease, which named it because of the parasitic concretions that looks like a stone. This disease is the formation in the tiny noludos hair, black or brown, with the hardness of a stone. They can be found all over the hair and are often situated within an inch of hair. The root is not never affected.

Tricornicosis nodosa:

This disease is often found in individuals who sweat a lot more often padecindola blondes than brunettes.

In examining the hair, especially the armpits, you see that are thicker than normal. They cite cases where armpit hairs have become black. Shaves these hairs can be parasites concretions around all or part of the stem, even the opening of the follicle. In other hairs alone the last third is covered with several nodes separated from each other well. Concretions adhere strongly to the hair, especially when dry. Come to give the hair 2 or 3 times its normal thickness. The central third of the hair is the most affected.


Polymorph is a disease caused by a parasite critogamicos series of the same family, called tricoptitos. These parasites, are composed of short elements, almost cubic and united in mycelia, by the appearance of parasites in the hair and around, distinguish the following major groups:

Trichophytum endotrix:

Is a group comprising only parasites that are found in the hair substances namely:

* Trichophytum acuminata.

* In cases of very advanced infections hairs seem completely filled with a mass of spores and chains together in parallel to the longitudinal axis. In some places there are so many spores accumulated in the hair cuticle and hair rise is literally about to explode.

In this case the spores tend to be more round than they are entirely out of the hair.

* Trichophytum pitting. It is in this group of parasites some mycelia on the surface of the hair but the largest group is in the interior of the hair itself.

* Trichophytum neo – endotrix. This group comprises proliferating parasites in the hair surface and reaching the substance. The group is divided into sub microsporones and megalosporones.

* Trichophytum ectotrix:

* Achorion (favorable)

It is the last group of parasites of the family of cryptogamic invading hairs.

The hair affected by favus, has the following characteristics;

Air bubbles of varying size in the surface of the hair containing the mycelia:

Longitudinal grooves in the hair substance, particularly in the aerial and shortage of mycelial elements and spores. These stakeholders are highly variable dimensions in the same hair. The affected hairs are a little more fragile than normal hair. Hairs contain favorable patients but relatively few mycelia. In the aerial part of the hair are sometimes hollow and slightly undulating grooves. These grooves are filled with dead spores and mycelia.

Pediculosis capitis:

It is a contagious disease of the hair, which is due to an infection called Pediculosis capitis incest. This puts a wealth of oval-shaped eggs that adheres tightly to the hair by chitinous secretions

The sudden narrowing:

According Niyogi this anomaly may be due to some unknown disease. In this case the hair diameter decreases sharply.

Other anomalies:

There are other stem abnormalities: double spinal, medullary abnormally high rates, deformed roots and protruding scales in the cuticular margin.

7. Hair analysis by neutron reactivation

This type of analysis is based on the principle that, in the materials being irradiated in a nuclear reactor, or other source of neutrons, some of the atoms of the substance is converted into radioactive isopotos:

The reaction from these elements comes from their energy and decay typical characteristic is specific and provide for identification and quantification.

The main advantages of such tests: Their specificity, its sensitivity and its ability to nondestructively with the specimen.

The ability to establish with any degree of certainty the identity of two samples or not, is based on purely statistical considerations as A. Traves depends on the following factors:

1 – Number of elements in trace reason, it is possible to analyze.

2 – Accuracy of analysis for each of these elements.

3 – The magnitude of the variation of the concentration of these elements among individuals deferens

4 – The reproducibility of the concentration of these elements in different samples of the same nature taken from the same individual.

Since 1962 revival neutron analysis has been successfully applied to the problem of individualization of human hair.

Javis and his collaborators showed:

a) That there is always human hair

8. Bibliography

Police technique. Barbera, Francisco A. and Turegano, John V., T. Editorial BLANCH, Valencia 1991.

Modern methods of criminal investigation, Soderman and O’Connell, Editorial LIMUSA Bogot 1992.

Hematology forensic and other serological techniques. Franco Ambriz, Editorial PORRUA Mexico 1991.

Research death ECHAZU, Dart. Editorial Police BA second edition 1983.

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