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Poroscopy (The following article is reprinted from the November 1982 issue of Identification News)
By D. R. ASHBAUGH, CPL The use of Poroscopy as a positive method of identification is rare, if not nonexistent today. The general feeling of identification specialists and others working in the field is that Poroscopy has little practical value due to the minuteness of its detail and the failure of pore structure to be reproduced consistently in crime scene and inked fingerprint impressions. The acceptance of this train of thought without challenge has, no doubt, allowed a valuable method of identification to slowly slip into oblivion. Approaching Poroscopy in a positive manner reveals that it is a competent method of identification in specific instances. It may be that these instances only account for less than 1% of the fingerprint identifications we make yearly. However, if Poroscopy is studied and practiced, it may be that another 1%, previously considered unidentifiable, will be found to be identifiable and suddenly a science which was previously thought to have little value becomes an extremely valuable tool to the identification specialist. Anyone entering the witness stand to give expert fingerprint evidence should be at least a little cognizant of the science of Poroscopy and the established scientific facts that have been documented in various journals over the years about the subject. Marcello Malpighi, Professor of the University of Bologna, was one of the first to examine pores and use a microscope in medicine. During 1686 Malpighi documented his observations of certain elevated ridges of the ends of the fingers are drawn into spirals. Upon examining these ridges with the microscope he observed and examined the open mouths of sweat glands. The invention of the microscope overshadowed Malpighi's findings of ridges and pores on the fingers until 1823 when Johannes Purkinje wrote a thesis at the University of Breslau. Purkinje mentioned a wonderful arrangement and curving of the minute furrows connected with the organ of touch on the inner surfaces of the hands and feet. Pores were not examined in detail until Dr. Edmund Locard of Lyons, France, published a paper in 1912, over 200 years after Malpighi's findings. Locard used Poroscopy as an independent method of identification and as an aid to reinforce identifications using the ridge characteristic method when the number of ridge characteristics were low.
According to Locard, the sweat pores vary in the following ways: (1) Size -- The size of the pores varies without system and several sizes of pores may be found along the same ridge or close to each other. Locard used fingerprint impressions to measure pores, rather than inked fingerprints, and found that pores vary in diameter from 88 to 220 micra (Micron = 1/1000 mm). The largest pores had three times the diameter and nine times the area of the smallest. (2) Shape -- The pores may be found elliptical, oval, square, rhomboid or triangular. Inked prints tend to have the pores filled in so that their shape is not clearly revealed. Accidental impressions developed with oxide or lead or an equally good substance, and then photographed to the proper enlargement, allows the individual shapes to be clearly seen. (3) Position on Ridge -- This is the most valuable feature of all and is the most conspicuous. The pores usually lie in a single row along the middle or crest of the ridge. Now and then a single pore or a series of them may open on the side of the ridge and actually appear to be positioned in the furrow. This is caused by the rounded shape of the friction ridge itself. The ink will adhere to the top of the ridge due to its height, which is the inner side of the pore, but not to the lower side of the ridge towards the furrow, which is the outer side of the pore. Therefore the pocket appearance in the inked print. On this very account one must not expect to find two separate prints of the same pore to be exactly alike in this respect, as the pore may be open in one and closed in the other in accordance with the amount of pressure applied. Again, the position of the pores may differ in their relative position to each other. A few may appear grouped together or spread apart. Occasionally two pores, may appear to be abreast on the ridge or they may be so close together that they appear to form a triangle. Such striking points are valuable as points of identification, but are also valuable in locating a fragment of a print in the complete known Impression. (4) Number and Frequency -- This feature is characteristic of an entire print or indeed of all the prints of a given individual and may be calculated in two ways: (i) The average number of pores that occur on a given length of ridge, and (ii) The average number of pores found within a given area. The amount of pores found in one centimeter of ridge varies from 9 to 18. Mathematically the positive agreement of some 20 to 40 pores should establish positive identity; yet where a larger number of details is obtainable, one should use his full opportunities and make the comparison cover some hundreds of pores or as many as are present. Using the above criteria, Locard aided many identifications made by the usual methods and in several cases has secured convictions by the unanswered testimony of the sweat pores.1 One of the cases I found documentation on was the Boudet and Simonin case in which Locard made corroborative use of Poroscopy at Lyons, France, in 1912. As to whether it was needed or not, I will leave to the reader. Locard described the case as follows: On June 19, 1912 the apartment of M. Chardonnet, at No. 6 Rue Centrale, was broken into and several pieces of jewelry together with 400 francs in money were stolen. There was no witness and no clue to the thieves; but a rosewood box in which the jewelry had been kept was literally covered with blurred finger marks. These were developed with carbonate of lead and photographed. On comparing these with the collections at headquarters an assistant named Chambon discovered that certain impressions belonged to a man by the name of Boudet who had been sentenced several times before for theft. On looking up the records, it was found that Boudet habitually operated with a pal named Simonin. The two were put under arrest and impressions of their hands, other than the fingerprints, were taken. There were obtained from the prints which covered the box, a fair impression of the middle phalange of the left middle finger of Boudet and one of a small area of the left palm of Simonin. From the ridges alone, in the usual way, there were established 78 points of identity for the first (Boudet) and 94 for the second (Simonin). Yet, as the accused would not confess, the case was brought before the assizes. Here the jury was shown enlarged photographs of the regions in question, taken both from the impressions on the box and from the men themselves, developed in the same way. In addition to the ridge details, emphasis was laid upon the correspondence of the pores of which, in the area from Boudet's finger, there were 901 separate pores. All of these, allowing for the difference in the amount of pressure, were shown to correspond exactly. In the area from the palm of Simonin there were more than 2000 such correspondences. As a result of this demonstration, which presented such an enormous number of correspondences, the jury was convinced and Boudet and Simonin were each sentenced for five years of hard labor. It is to be emphasized first that there was absolutely nothing else than the marks on the rosewood box that could be brought up against the men and secondly, that the box had been so much handled by the thieves that there were no distinct patterns and but few impressions. Locard further remarks that without the slightest doubt the sweat pores played the principal role in convincing the jurors who could not deny this overwhelming mass of evidence. If a jury or magistrate hesitates because it may seem audacious to believe that 12 to 15 points are sufficient to identify an impression, they will do so no longer when they are shown the perfect accord of hundreds of pores. A second case that Locard contributed to, where I could find some documentation, was the Maten case, also from Lyons, France. A fragmentary imprint without details (ridge characteristics) contained 200 pores and was thereby identified as coming from the right ring finger of the accused burglar Maten. In an article on Poroscopy published in 1914, Locard closes with the following conclusion: (1) The sweat pores present the triple characteristic of perpetuity, immutability and variety which establishes them as a means of identification of importance. (2) Identification by the comparison of pores in a striking manner confirms the evidence from fingerprints by adding to the determination of ridge details that of the visible sweat pores, the number of which is often many hundreds and in a good impression may exceed a thousand. (3) In most cases in which the digital or palmer impression is too fragmentary for an absolute identification by the dactyloscopic method, which required a minimum of twelve characteristic points, the comparison of pores, providing these are discernable, will permit the attainment of positive identification. Locard apparently made other Poroscopy identification, for in Personal Identification, by Wentworth and Wilder (1918), Locard's work was commented on in detail and the following passage is within that script: “This method of identification by sweat pores of Poroscopy has now been, for some time, in practical use at the Prefecture of Police at Lyons, France, at the hands of Dr. Edmund Locard, the Director. By this means he has aided many times an identification made by the usual methods and in several cases, notably the now famous one of Boudet and Simonin, has secured a conviction by the unanswerable testimony of the sweat pores.” The fact that Wentworth and Wilder included Locard's work in their book and commented positively about it certainly adds great credibility to the science of Poroscopy as Harris Hawthorne Wilder, Ph.D., devoted his studies to morphology, the methodology of plantar and palmer dermatoglyphics, inheritance and racial differences, while Bert Wentworth had been a Police Commissioner, a good combination of science and law to examine such work as Locard's. Personal Identification also makes several valuable contributions to the science of Poroscopy. Wentworth and Wilder explain how, during the fourth month of intrauterine life, friction ridges are formed on the hands of the fetus. The following is as a result of studying how the ridge itself is formed and suggests that the reader observe this phenomenon along the edge of the friction ridge pattern area where the ridged skin and normal skin meet on the second joint of the index finger. In this transition region the ridges are seen to begin as separate islands, placed in a row, gradually melting into one another until the typical ridge is attained. (This can also be noticed along the edge of rolled inked impressions when rolled to their extremities). Thus (1) from the existence of the sweat pores along the ridges at approximately equal intervals, (2) from the presence of very short ridges, the so--called islands, containing a single sweat pore; and of others, plainly made up of two or three islands and showing a sweat pore for each unit and (3) from the appearance of the ridges at their beginnings on the transition area, where they can clearly be seen to consist of rows of islands in all degrees of fusion, and where all stages are seen, from distinct islands to a completely formed ridge, it becomes evident that the friction ridges are formed by the fusion in rows of minute round or oval structures, each having a single sweat pore in its centre, so that the sweat pores occurring along a ridge indicate the number of separate unit islands of which it is composed. The text goes on to say that this explanation of the composition of the ridges is confirmed by a comparison with the condition found in other animals. Wentworth and Wilder further comment, “As seen on the surface of the skin at a low magnification, the sweat pores are found to vary in so many ways that after studying a small area for a while, certain ones of them and certain groups will take on an individuality as great as do the ridges which bear them, and because of this each small area may be distinguished absolutely from any other. In fact, we have in these minute structures a set of objects upon which, notwithstanding their minuteness, the positive identification of a small patch of friction skin can be based, and this surely can be done with the ridge details in the normal way.” They further comment that, “We have, then, in the sweat pores, with their great individual differences, and their persistence throughout life, an invaluable series of individual features, which can be employed to advantage in cases where the record is too incomplete to show a definite pattern, or too fragmentary to make out even the ridge details with certainty. As compared with one case where definite finger patterns are left upon the premises, there are dozens where only the marks of a few ridges can be obtained and these often are of other parts of the hand than the finger bulbs. Such fragments may be often identified by Poroscopy if we have for comparison the prints of the corresponding parts of the hands of suspected persons. Wentworth and Wilder wrote the following in closing their chapter on Poroscopy, which has a familiar ring to it, “Identification by the sweat pores has been used but little up to the present time, perhaps mainly by Dr. Locard in France and by the present authors in the United States, but the suggestion that this field is still largely unexplored may induce others to experiment and investigate along these lines.” The majority of fingerprint texts published after Personal Identification devote little space to Poroscopy, mainly because there was little research done in the field. The lack of interest in Poroscopy is blamed on its so--called short--comings. The major short--comings of Poroscopy in the past have been stated as “(1) powder fill in of pore structure of crime scene fingerprints, (2) poor inked impressions for comparison due to improper pressure or improper inking, (3) lack of adequate visual aids to examine pore structure, (4) location of pores to be compared, (5) the low percentage of fingerprints displaying pore structure when developed on inked, and (6) the degree of study required to gain expertise in Poroscopy and the time required to make a comparison and hopefully an identification. Some of the pitfalls have been rectified while others have been improved. Training will improve the remaining to such a degree that on the whole we should be taking another look at the science of Poroscopy as a means of identification. I would like to comment on the above short--comings in order: (1) Powder fill is still somewhat of a problem, even with modern powders. However, careful brushing can improve results. Careful cleaning of the fingerprint after photography can improve the clarity of the pore structure if it was there in the first place. One of the simplest ways to improve results is proper powder care by insuring no moisture contaminates the powder jar since this causes a globing effect of the powder on the latent fingerprint. (2) The use of pre--inked fingerprinting strips has increased the clarity of inked impressions in the field. Where glass slabs are still in use, a small amount of training and practice in inking the slab will improve results. Demonstrations and practice on correct pressure when fingerprinting will also be an asset. (3) The arrival of the microscope in the identification section has been a tremendous boost as far as visual aids are concerned. This piece of equipment is allowing us to examine fingerprints and other physical evidence as never before in the section as well as allowing research to take place in various fields as Poroscopy and Edgescopy. Sections without microscopes can make initial comparisons under a fingerprint glass and, if promising can go to enlarged photographs for final comparison. (4) To search pores we must still depend upon the surrounding ridge characteristics or suspects submitted by investigators. (5) Pore structure does not appear on all developed or inked fingerprints nor will we require use of Poroscopy alone on a large number of crime scene prints for identification purposes. However, a knowledge of Poroscopy will allow us to add strength to low ridge count identifications, assist in evaluating ridge characteristics and, on occasion, make identifications on prints we previously considered unidentifiable. Even inventions as new and versatile as the LASER are only used in certain cases when some criteria is met and not required in all cases. Something I have noticed is that developed crime scene fingerprints that display pore structure usually have a donor finger that, when inked and printed properly, displays pore structure in the inked print also. Therefore, that piece of fingerprint that is considered unidentifiable, due to a lack of ridge characteristics, but displays ample pore structure, may be worth collecting anyway. (6) Learning the basics of Poroscopy is not all that time consuming as the material is minimal at this point and the bulk of it is printed here. The study to gain expertise in the field takes time and experience but as identification specialists we are examining fingerprints everyday. Examine pores when possible during your daily work and soon they will catch your eye as do ridge characteristics. The time for comparison depends on experience, clarity of pore structure, etc., and is not a factor if we are sincere in our work in the identification field. Poroscopy is an older method of identification that is hopefully being renewed and in great need of further study. With this in mind I set about to familiarize myself with pores to ascertain if I could see Locard's axioms dealing with relative position, shape, numbers and size of pores for comparison purposes. As Locard did not have, or did not publish, any mathematical formula for arriving at the figures for positive identification at between 20 to 40 pores in agreement I felt an attempt to ascertain how these numbers were arrived at would give me considerable exposure to pores as I must first find out how many pores can be on the friction skin in the bulb area of the finger, first hand. To do this I had to count the pores on rolled inked impressions. I selected fifty clearly rolled inked prints from our local fingerprint file, attempting to find prints rolled from nail edge to nail edge that of course, displayed clearly reproduced pore structure. The fingerprints were enlarged to 5" x 7". Using a fingerprint glass I counted the pores, touching each one with a fountain pen so I knew which ones I had counted and where I was on the fingerprint should I be disturbed. While counting I was observing (1) consistency in size of the pores throughout the fingerprint (2) shapes of the pores as to variety and visibility, (3) position of the pores on the ridges and if there was a pattern or were they randomly placed, (4) the number and frequency of pores in a specific area and (5) finally and most important, are pores really a reasonable and valid means of identification and can I compute any mathematical method as a guide to a minimum of pores that should be examined before an opinion can be formed. This number, of course, would be a guide only as all fingerprint identification is, in fact, a physical match.
From the counting and examining of pores on the various rolled inked impressions,
I came to the following conclusions on which I would like to comment on
in order, as previously mentioned. (1) The size of the pores varied within the fingerprint to a degree. I found some prints had all small pores which varied in size also throughout the print, while other prints had coarser pores which also varied in size. Occasionally an extra large pore would stand out from the others and the ridge around it would bulge. The pores do vary in size; however there is a general tendency throughout the fingerprint for pores to be similar in size, and as far as being generally large or small. (2) The pores were a variety of shapes. However, only the obvious differences were observed due to my method of examination. Had I studied these prints under a microscope, I feel more shapes would have been noticed. By obvious differences I am referring to a round pore being beside a triangle or oblong pore, and this would catch my eye due to the great difference. Pores do have different shapes from my observations. (3) The positions of the pores were random. I could see no rhyme or reason for pattern associated with location. I did find some prints would have pores that were reasonable orderly on the ridge with areas of mass confusion in placement, and then I found prints where most of the pores were positioned all over the place. From my observations, I feel pores appear randomly on the ridge and that some fingerprints can generally have more erratic placement of pores than others. (4) The number and frequency of pores is an area where I can only give a generalized opinion from my observations and no statistics as Locard did. I found that the fingerprints displaying small pores appeared to have finer pores or pods and appeared more frequent in a given area, while the larger pores had larger pore units and appeared fewer times in a given area. I did not measure a length of ridge and count the pores, but just estimated the distance. I did find that in some sections of a ridge the pores would be jammed together while in other sections the pores would be spread apart.
(5) As far as pores being a valid means of identification, I feel that Locard
has proven this by his court appearances and studies. All of my conclusions tend to agree with what Locard stated in papers during 1912 and I have satisfied myself from my observations that Locard, as well as Wentworth and Wilder, when they spoke of Poroscopy, were dealing with a valid form of personal identification. The comments of Locard that 20 to 40 pores in agreement was sufficient for positive identification was the one issue on which I could find no data. I am not a mathematician, but I attempted to calculate how many pores were required before one could consider forming an opinion when comparing pores. First of all, I would like to re--emphasize that fingerprint identification is a physical--match where the examiner forms an opinion from evaluation and does not count the number of ridge characteristics in agreement. With pores this is also true. However, we have a situation where we have a row of units, each sporting a pore somewhere on its surface. Imagine drawing a line from pore to pore along the ridge. The resulting line would zig zag back and forth along the ridge from pore to pore, as would a break line on a jagged piece of metal. The fact that some pores are closer together than others gives us a second dimension. Not only will this line zig zag, but the lengths between each pore will differ. Establishing a formula for this type of situation is not so difficult and there are added safety features which I will explain later. If Wentworth and Wilder's account of the formation of ridges is correct, then each pore unit or pod has a pore randomly placed on its surface. For our purpose we will divide the pore pod into five general areas, being the four sides and the centre, similar to the positions of spots on the five side of dice. Therefore the chance of any one pore unit having its pore surface on either side of the centre, or on either lateral end of the pore unit on the ridge, is 1:5. The chance of two units side by side or across from each other having pores surface in the same posts is 1:52 or 25. The chance of 20 pore units having their pods in the same relative positions is 1:520) or 1:95,367,400,390,625, which is just over 1:95 trillion. The chance of 30 pore units having pores in the same relative position is 1:530 of 1:921,947,269,439,697,265,625 which is just over 1:921,947 quadrillion. During June of last year the United Nations estimated the total world population had reached 4.4 billion people or a possible 44 billion fingers. From counting pores on various rolled inked finger impressions I found the number ranged from 1611 pores on smaller fingers to just under 2700 pores (2658) on the larger thumb print. Considering the largest thumb print I examined was not the largest thumb print that I have encountered, I looked elsewhere for the maximum possible number of pores one would likely find in a large thumb print or fingerprint. In Scott's Fingerprint Mechanics (Robert D. Olsen, Sr., 1978) it is said that pores appear on friction skin 2700 times in every square inch approximately. The thumb print in which I counted 2658 pores was close to the size of one square inch. The other fingerprints I counted had a number of pores that was proportionate to its size in relation to the approximation of friction skin having 2700 pores per square inch of surface. I therefore used this number as the number of pores that one would likely find in about one square inch of friction skin. The largest thumb print I have encountered would be just under two square inches of surface, or an estimated 5000 pore units on the bulb area friction skin. This is, of course, double the amount of pores found on some fingers and again possibly through over estimation, is a safety factor. Considering there are 44 billion fingers in the world at present, give or take a few, there could be up to 220 trillion pore units on fingers, in the bulb friction skin area of fingers in existence in the world today. The chance of thirty pore units having pores in the same relative position in a row or on adjacent ridges is 1:921,947 quadrillion which is more than 41 million times the amount of pore pods in existence on the ends of fingers in the world. There are some things I did not take into consideration with the above calculations and they are size and shape of pores, presence of ridge characteristics on adjacent ridges or part of the actual ridge being compared. These all, if present and being in agreement during the comparison, would sky rocket the chance factors. As I stated earlier, I am not a mathematician and only basically understand how these problems are solved. However, my calculations tend to support Locard's claim that between 20 and 40 pores in agreement is sufficient to form an opinion on positive identification with Poroscopy. One of the problems not covered yet is that on occasion during comparison some of the pores fill in with developer or just fail to reproduce. How should this matter be dealt with? Locard's opinion on the subject is quite simple. A pore filled in or not recorded was not considered a point of disagreement as it can be explained. The fact that the area the pore should appear in is not evidence to the contrary, then it can be assumed that the pore is filled in, however it was actually there. This would not be too common on occurrence or the value of the comparison itself would be in doubt. These fill--ins can also be worked around using surrounding pores. To compare pores I use a microscope to examine the inked impression and the fingerprint glass to examine the crime scene print or an enlarged photograph usually taken at the scene. If this initial comparison shows promise, I then go to the enlarged photographs of both impressions, enlarged to a diameter that shows pore detail. Knowing the difference between enlargement and magnification is important. Too much magnification will cause the pore edges to melt. Photographs taken with the microscope should be done at lower magnification and then enlarged in the photo enlarger. To compare two photographs, I use small dividers and make comparative measurements as to relative position of the pores to each other as well as visually comparing their size and shape. Using ridge characteristics as focal points and comparing pores from ridge character to ridge character makes the comparison easy to control. All pores should be examined that are available. As of now I have compared the pore structure of crime scene prints that I have identified by ridge characteristics and have found that pressure distortion can change the basic shape of the pore itself. An overall examination of the amount of pressure placed on the ridge should be made prior to your detailed examination so that you will be somewhat aware of the type of distortion you may encounter. This overall assessment of pressure is easier to see throughout a general area of the fingerprint rather than at the pore unit level. Identification sections with the Bausch & Lomb microscope can turn the head around in the stand and by using the stand backwards a small shelf is directly under your eyes for fingerprint impressions and a fingerprint glass. A 4" x 5" glass negative holder under the microscope holding the inked impression allows you to use finger pointers without damaging the fine detail in the fingerprint. Poroscopy requires a reasonable amount of study and experience prior to one reaching a level of expertise where a court appearance on Poroscopy alone is advisable. The use of Poroscopy while evaluating ridge characteristics is an excellent training ground and after study of the science it can be used to reinforce identifications of low ridge characteristic prints. The process of evaluating a ridge characteristic pore unit to pore unit will definitely enhance any opinion that you form about a single ridge characteristic or a ridge characteristic in sequence. Poroscopy is not new. It has been accepted and used in courts. It has a scientific basis and can be extremely valuable in specific instances. Yet it is in a stage of renewal and caution should be used to ensure one's knowledge of the science is sufficient to form competent opinions.
I am certain that with the arrival of microscopes in the identification
sections, modern latent fingerprint development methods and an adequate
educated and trained identification specialist, Poroscopy will be an everyday
tool in fingerprint identification in the immediate future. BIBLIOGRAPHY 1. Personal Identification, Wentworth and Wilder, 1912, p 28 2. Fingerprint Techniques, Andre A. Moenssens, 1971 3. Scott's Fingerprint Mechanics, Robert D. Olsen, Sr., 1978
4. Finger, Palm and Sole Prints, Salil Kumar (Editor--—The article “Poroscopy -- An Overview” in Issue # 4 this year served as an introduction for this topic. I hope this article provides you either a substantive review or the start of a good literary foundation. David Ashbaugh of the R.C.M.P. has made many literary contributions to our science. All of his papers have such depth--—they deserve repeated readings and thorough study.)
This article was reprinted in “THE PRINT” |