In the following we will consider the philosophies of traditional Chinese medicine (TCM), how and why many veterinarians now are using acupuncture, the illnesses commonly treated with the technique and the competing scientific theories that attempt to explain it.
An Ancient Art
In the narrowest sense, acupuncture is the application of small-gauge needles to various points on the body for the purpose of eliciting physiological responses in the treatment of almost any disease or condition, and it seems especially useful for relieving pain. In a broader sense, acupuncture is an ancient procedure used in TCM for the treatment of whole-body conditions.
No one really knows when or where it started, but it has ancient roots. A primitive acupuncture-like therapy was practiced in India some 7000 years ago, and Stone Age humans used fishbone needles in China 5000 years ago.(1) A large body of written information about the practice has survived the ages and grown with time (2).
One of the earliest records of veterinary acupuncture was some 3000 years ago in India for the treatment of elephants; however, the father of veterinary acupuncture generally is considered to be Shun Yang (480 BC) from China. The earliest American medical journal reference the authors could find to acupuncture's use in human medicine was in 1836; however, European writers of the late 1600s had published on the subject earlier (3,4). Interestingly, Sir William Osler, who taught at Harvard and Yale and who gave the world its current residency system of medical education, wrote of acupuncture in 1892 (5). The procedure did not make it into the New England Journal of Medicine until 1926, but these references were positive, indicating that acupuncture could be an appropriate and useful medical technique.
The procedure had been used for a variety of illnesses, but it began to fall into obscurity in the 1940s in the United States as people turned to newly emerging, potent, increasingly ailment-specific antibiotics to treat their health problems.
In 1973, The American Medical Association Council of Scientific Affairs declared acupuncture an experimental medical procedure. The increased interest was due in no small part to Richard Nixon's efforts to improve relations with China, where acupuncture was and still is a common practice. In fact, James Reston, a member of Nixon's press corps in China, had surgery using acupuncture as an anesthesia, which later was widely reported in the press. By 1983, the American Osteopathic Association endorsed the use of acupuncture as a part of medical practice.
Although acupuncture terminology still is largely based on philosophy, it has become apparent that the scientific method has crept into the practice with the result that the Western veterinary and medical establishments are less able to discount acupuncture as a pastime of shamans.
Along with acupuncture's increased use in human medicine, veterinary acupuncture has moved closer to mainstream practices. It also might be said that the mainstream has moved closer to acupuncture, given that chapters on acupuncture now are standard in many major veterinary texts. In addition, acupuncture has become a big business worldwide. Today nearly 3 million veterinary and medical practitioners, assistants and pharmacists are trained in acupuncture. Of this number it is estimated that 150,000 are veterinarians and 700,000 are paraveterinary assistants.
The IVAS has become the primary professional society for veterinary acupuncturists in the United States, complete with a newsletter, a journal and a World Wide Web site. http://www.ivas.org
An Eastern Perspective
To understand the basics of acupuncture it is important to comprehend the tradition out of which it developed. In TCM, animals and humans are viewed as tiny parts of an infinite universe subject to laws that govern all living and nonliving things. The fundamental concept is that an animal or person who follows these general laws of nature will reap the benefits of good health.
Acupuncture is not a stand-alone procedure in this framework; rather, it is a part of a much larger medical system encompassing acupuncture, moxibustion (the burning of moxa, a soft downy material, on the skin in the treatment of various disorders), massage, breathing exercises, nutrition, herbal medicine and even philosophy of life (6).
The goal of TCM is to diagnose imbalances in the life force (Qi), determine their causes (etiology of the disease) and subsequently remove those causes from the patient's environment (treatment). TCM views disease as an imbalance between two polarities of Qi, yin (-) and yang (+). Within this conceptual framework, acupuncture is used to "communicate" with body organs and tissues through special channels or meridians. (There is no known physiological equivalent to these energy pathways.) Health and healing in this context is the integration and restoration of balance or harmony of Qi. This view has been validated most recently by the discovery of the relationship between brain chemistry and the immune system. Some critics assert that Western medicine has a mechanistic view of health, reducing disease and illness to specific cellular and molecular systems. Outstanding medical advances have been made using the western viewpoint, but, according to the Eastern tradition, the sum of the whole body still is greater than its parts (6).
The effectiveness of many traditional acupuncture points has been determined experimentally. Some 670 of them have survived the test of time. In her book, Between Heaven and Earth, Harriet Beinfield proposed an analogy: "comparing an acupuncturist with a Western veterinary or medical practitioner is similar to comparing a gardener and a mechanic" (7) The gardener considers the totality of his or her plants' environment (sunlight, density of planting, types and amounts of fertiliser, temperature, water, etc.), whereas the mechanic searches to replace or repair a dysfunctional component.
Theories In Practice
To illustrate the differences between the Eastern and Western philosophies as they relate to veterinary medicine, let us follow a hypothetical canine patient while she is being examined by a Western-trained clinician and compare this to the procedures used by a practitioner of TCM. An owner makes an appointment because her previously housetrained female dog recently has started having "accidents" in the house, and she wants to rule out a medical basis for the problem before she addresses it as a behavioral issue. Both practitioners will be presented with the same symptoms, but their methods of diagnostics will be completely different.
At the traditional vet's office, the dog is placed on the examining table, and the vet asks questions about the frequency and quantity of urination. While the owner is talking, the vet takes the dog's temperature and then begins to perform a physical exam that includes listening to the heart and bowel sounds and palpating the abdomen to check for any masses. The vet suggests several lab tests to rule out a urinary tract infection and other more serious diseases such as diabetes mellitus and diabetes insipidus. The total focus of the appointment is to address the clinical symptoms. In contrast, the vet trained in TCM asks questions about the dog's behavior and previous history, which may be similar to the questions that the traditional vet asks, such as: "Does the dog drink small or large amounts of water at one time?" "When did the behavior start to occur?" and "How often does it happen?"
The practitioner then goes on to ask what may seem to be unrelated questions. Does it happen more frequently at a particular time of the day? Does your pet choose to sleep in the sun, or does she seek out a cool, shady spot? Does she like to lie on a soft surface, or does she prefer to sleep on a firm supportive surface?
By now the owner may become impatient with answering detailed questions that do not appear to have anything to do with the problem. But to a practitioner of TCM, these questions are all valid because the patient is an individual made up of physical, mental and emotional components. Questions are asked about the dog's environment, her diet and favorite foods, stressors and behavioral tendencies in an attempt to consider the "whole," just as the gardener considers the totality of his or her environment.
While the owner is relating this information, the TCM practitioner observes the animal's behavior in the exam room, checking her tongue, looking at the dog's body shape and examining her skin and coat. The next part of the exam includes listening to the chest with a stethoscope and taking note of the breathing sounds and the character of her bark.
Just like the Western clinician, the TCM practitioner then palpates the abdomen and limbs. In addition he or she will check the dog's pulse (which provides information about organ systems and their locations on energy pathways) and also will assess specific areas along the back, sides and abdomen. In this tradition these diagnostic points correspond to specific internal organs.
Finally, the TCM practitioner smells for specific odors emanating from the eyes, nose, ears and mouth, which all play a part in the diagnostic process.
The Acupuncture Procedure
The lab tests suggested by the traditional Western vet rule out the serious diseases associated with urinary incontinence, and the diagnosis indicates oestrogen-responsive atrophy of the muscle of the bladder wall. The allopathic vet probably will prescribe dosages of DES (diethylstilbestrol), a synthetic oestrogen, to maintain bladder tone. Although DES is indicated for the treatment of this kind of incontinence, it has many possible side effects, including skin and liver problems and mammary tumours.
The difference between the allopathic system of treatment and the system of TCM boils down to this: In Western medicine, the same disease or condition normally is treated the same way in all patients; in TCM, the same condition may and most probably will be treated differently in different patients because the underlying causes may differ.
In TCM, frequent urination or incontinence usually stems from a weakness in the kidney yang, which can cause an overall deficiency in the Qi. Incontinence also is a function of the Qi associated with the spleen, because it is believed the spleen keeps organs functioning properly and can be stimulated to treat herniations, prolapses, etc.
Treatment most likely would consist of using needles to elicit a physiological response by stimulating specific anatomic loci, in this case, along the bladder, kidney and spleen meridians. The size of the animal and the location of the points being treated determine the length of the needles used. A short needle, about 0.5 inch, is used in points located over bony areas such as the head or face. The most common size used is about 1 inch long. For larger dogs or for deeper penetration, there are longer needles available (1.5-2.0 inches). The needles are solid and very flexible, and presterilised disposable ones are an option.
In the hands of a properly trained clinician, the animal does not appear to have any discomfort at all. Inserting the needles to the proper depth and angle, manipulating them during the treatment and removing them all are techniques that can be achieved only through training and extensive practice. This is why it is so important to consult a properly certified veterinary acupuncturist.
In the general treatment of ailments, it may take four to eight sessions to know if acupuncture therapy will be effective, although a response could be seen even after the first treatment, and improvements often are noticed after the third. Treatments may last from 10 seconds to 30 minutes and may be recommended once or twice weekly. The long-term goal is always to fix the number of treatments to the minimum required for effectiveness. This may be every six months for arthritis or could be as often as every two months for other conditions. Both frequency and duration of treatment depend on the animal and the ailment.
What Can be Treated?
In addition to incontinence, acupuncture, in conjunction with TCM or the body of Western medicine, may be considered supportive or adjunct therapy for a vast array of other conditions. Notice of the procedure's versatility was boosted with tests of its effectiveness in humans. The University of California, Los Angeles, conducted the Acupuncture Research Project from 1973 to 1980. When the study began it was viewed as little more than a curiosity-until the findings started trickling in.
At the outset, medical opposition was high and resolute, especially from orthopedic surgeons. Public acceptance was more immediate than acceptance by the medical community. Satisfied patients referred friends, and eventually the waiting list was six weeks for an appointment. The UCLA Acupuncture Research Project found various forms of acupuncture were effective for pain relief for various orthopedic, obstetric and surgical procedures; treatment of chronic pain; sensorineural hearing loss; compulsive disorders such as obesity and tobacco and drug addiction; and bronchial asthma.
In other studies conducted on both humans and dogs, acupuncture was found to be beneficial in cases where analgesics and anti-inflammatory medications had been ineffective or had demonstrated side effects and in cases where surgery was not recommended. For example, many practitioners are pleased with the results of acupuncture in treating arthritis in both humans and canines. One study found that acupuncture enhanced the efficacy of antibiotic treatment for canine otitis crises (8).
Favorable acupuncture results have been reported in the treatment of many other canine conditions, including the following: cardiovascular disorders (9), chronic respiratory conditions (10), dermatological disorders (11), gastrointestinal disorders (12), gynecological disorders (13), immune-mediated disorders (14), male reproductive disorders (15), musculoskeletal disorders (16), neurological disorders (17), reproductive disorders (18), thoracolumbar and cervical disc disease (19, 20). Deciding if your dog should be treated with acupuncture therapy often depends on the dog itself and the condition afflicting it. "My attitude is that with each and every animal with each and every condition, you look at what the best comprehensive integrative approach is and develop a therapeutic plan for that animal," explains Allen Schoen, DVM, co-editor of "Complementary and Alternative Veterinary Medicine: Principles and Practice" (Mosby 1998). "Sometimes acupuncture is used as a last resort; at other times it may be chosen as the first approach [for example] if surgery would have potential complications, and only if acupuncture didn't work would you consider surgery."
According to Schoen, before you decide on any treatment approach, it is important to get a good diagnosis and then look at all the options, including acupuncture and those offered by conventional medicine. He suggests obtaining a traditional veterinarian's opinion and diagnosis before deciding if acupuncture should complement the treatment of veterinary disorders.
Schoen explains there are some situations in which acupuncture may not be effective or should not be used. For example, extremely anxious pets sometimes can be so excitable that the release of their own adrenaline counteracts acupuncture's benefits. Owners also should be aware of specific medical complications. "[Acupuncture] normally does not interfere with other conventional approaches," he explains, "but certain medications, such as corticosteroids, can decrease the effectiveness of acupuncture. [In addition,] you want to be exceedingly careful in using acupuncture with cancer because selecting the wrong points can actually accelerate the cancer growth."
Because of this, in Schoen's opinion, only someone who is trained in both veterinary medicine and veterinary acupuncture should treat your pet if you are considering acupuncture as an alternative therapy.
How Does it Work?
Now that we've explored the philosophy behind acupuncture and some of those theories in practice, you may be wondering about the science behind the technique and if there is any clinical evidence of efficacy that will withstand modern Western scrutiny. The answer is a qualified "yes." Some modern practitioners feel that at its most basic level, acupuncture is applied neurophysiology. We may one day be able to explain acupuncture in those terms. Today, Western science still has a poor understanding of its mechanisms. However, the body of anecdotal evidence supporting its effectiveness is overwhelming. One only has to watch surgery under acupuncture anesthesia to comprehend that something significant and unfamiliar to the Western way of thinking is going on. The World Health Organization concluded in 1979 that "Acupuncture is clearly not a panacea for all ills but sheer weight of evidence demands that acupuncture must be taken seriously as a clinical procedure of considerable value."
Acupuncture has had field tests, too. Some 4000 years of application on a sizeable segment of the world's population makes acupuncture arguably the most widely practiced and thoroughly tested medical technique in history (21).
In 1998 the American Veterinary Medical Association took this position in its "Guidelines for Complementary and Alternative Veterinary Medicine" approved by the American Veterinary Medical Association: "Veterinary acupuncture and acutherapy are considered an integral part of veterinary medicine. These techniques should be regarded as surgical and/or medical procedures under state veterinary practice acts. It is recommended that educational programs be undertaken by veterinarians before they are considered competent to practice veterinary acupuncture."
Besides acupuncture courses that currently are available, there also are some popular textbooks including Veterinary Acupuncture by Alan Klide and Shiu Kung (22). A more recent book is Veterinary Acupuncture: Ancient Art of Modern Medicine (23). For a more general, TCM text suitable for the layperson, we suggest Four Paws, Five Directions by Cheryl Schwartz (24).
To understand how the theories of acupuncture translate to pain relief, it is necessary to know a little about how pain is transmitted and experienced by the body. Pain is a double-edged sword. On one hand it protects us from damage by warning us of harmful situations, but in chronic conditions it is as debilitating as the disease process itself. Abnormal chronic pain states are thought to result from damage within the pain pathway itself, either in the peripheral nerves or the central nervous system.
The normal protective pain mechanism, which warns of impending or actual damage, is activated by mechanical, heat or other noxious stimuli impinging on pain receptors that then transmit the pain impulse to the CNS through afferent nerve fibers. Unlike other sensory input, pain recognition is subjective, and previous experiences can influence one's perception of it. This is true of dogs also; some breeds generally are more stoic than others. Pain perception also is a function of sex as females have shown a much higher pain threshold.
How is this possible? The body has its own pain-suppression mechanisms. This built-in analgesic system depends on the presence of endogenous opiates, which include endorphins. Most Western theories suggest acupuncture either instigates the production of these opiates or blocks pain transmission. Not unexpectedly, when East meets West and when philosophy meets science, confusion undoubtedly will occur. Similarly, when old meets new, questions of quackery from both sides will arise. Even in light of this, some Western theories have sought to explain the reported pain-relief benefits of acupuncture. One of those is the gate or inhibition theory, which proposes that pain is blocked by stimulating sensory neurones that travel faster than those that transmit pain (25).
Several types of nerve fibers are involved in pain transmission. As mentioned before, there are three types of pain receptors. Stimuli received from the mechanical and thermal pain receptors are transmitted over large myelinated A-delta fibers at a speed close to 30 meters per second. Impulses received by the other type of receptors travel much more slowly on the C fibers at the rate of 12 meters per second. A-alpha fibers, which are necessary for the proper perception of where we are in three-dimensional space, i.e., where our feet are located, are found in muscles and joints. Alpha-beta neurones are involved in feeling light touch and the bending of hairs. A-alpha and A-beta fibers transmit nerve impulses many times faster than A-delta or C fibers. AP stimulation may induce non-painful sensory information that travels along A-beta fibers. When the information reaches something called the inhibitory interneurones, it shuts a nerve transmission "gate" that blocks the conduction of the slower travelling A-delta and C fibres.
The gate theory may account for some part of the mechanism of acupuncture analgesia, but it does not explain the delayed effects of treatment or the results of cross-circulation studies (studies in which the blood circulation of two animals were connected, and the procedure performed on one produced results in both). These factors are much better explained by the competing humoral theory, which states that acupuncture instigates the release of endogenous (developed from within) opiates that produce a self-induced analgesia (26). In other words, acupuncture may work by stimulating specific afferent nerves, which in turn activate a spinal cord center, a mid-brain center and the hypothalamus/anterior pituitary unit. All three of these have been shown to block pain transmission by means of endorphins and/or other analgesic neurotransmitters. Some believe that acupuncture's pain relief derives from a combination of the neurological and humoral explanations (27).
Another theory suggests acupuncture may have localized vasodilatation effects, which would explain the procedure's benefits specific to musculoskeletal disorders. Dilated blood vessels are better able to eliminate pain-producing substances such as bradykinin (a substance released from blood plasma by some snake venoms and certain other enzymes that lowers blood pressure and triggers pain), prostaglandins and other inflammatory products.
Another explanation is the autonomic theory, which maintains that internal organs can be stimulated by external acupuncture points that selectively excite parasympathetic and sympathetic nerves regulating the autonomic nervous system (28).
The bioelectric theory tops off this confusing mix of theories. It suggests acupuncture meridians are like direct current pathways and acupuncture points function as amplifiers. What these theories have in common is the stimulation of acupuncture points via insertion of small needles, application of pressure, cupping (suction) and application of heat through moxibustion (which can be used to raise the temperature of the needles), or infrared, laser or electrical stimulation.
Interpreting Scientific Studies
Although acupuncture's successes have been tested in practice throughout history and have attracted a following of practitioners and patients, rigorous scientific acupuncture trials have yielded mixed results. Unfortunately, there is no tight control of patient suitability/responsiveness or practitioner expertise, and even studies with statistical analyses may be flawed because of inappropriately small or non-random samples. One well-known text used to teach biostatistics to medical and veterinary students maintains that in general, major errors are made in the statistical treatment of data in at least 50 percent of all the papers submitted for peer review in journals (29). Significant efforts have been made to improve the validity of statistical inferences drawn in journal articles.
Flaws in the statistical treatment of experimental data especially are damaging in clinical studies. Veterinarians and physicians consider their treatment options (including acupuncture) based on the outcomes of clinical trials. If erroneous conclusions are drawn from experimental data, patients may be exposed to unnecessary risks, discomfort and expense. Worst of all, more efficacious treatment may be delayed or not even attempted. It is therefore important to read the claims made about acupuncture with a discerning eye. This is not to say the use of statistics is an invalid and unrecognized strategy, but be aware that errors can be made in both the experimental design and in the conclusions drawn, so what you read always must be questioned with those caveats in mind.
Some detractors absolutely are convinced that acupuncture is little more than "nonsense with needles" and hope it will pass from the contemporary scene and fall into disuse like other obsolete treatments such as purging, leeching and bleeding (30). A lack of evidence, however, is not proof that a treatment is not effective. In the words of a colleague, "If there are no benefits derived from the process, acupuncture would have to be categorized as one of the longest playing scams in the history of mankind (31)".
We have barely scratched the surface of this complex and controversial subject. However, we hope you take away from this article the following:
1) Acupuncture can be a beneficial adjunct therapy, but it has its own set of dangers, not the least of which is the possibility of a lack of diagnosis or misdiagnosis of problems that routinely would be identified in Western veterinary medicine;
2) Anecdotally, acupuncture works, so if you do choose to take your dog to a veterinary acupuncturist, take it to someone who is having success in treating similar problems;
3) if Western medicine has failed your dog, there is little to lose in trying acupuncture. But do not expect it to be the miracle cure; it is not a panacea. In the hands of some practitioners, however, it has produced successes that are hard to explain using the principles of our current scientific and medical knowledge.
John Cargill, Retired Officer of Marines, statistician and science writer, grew up with Airedale Terriers and American Foxhounds but lives on a boat in Florida with his 5-year-old Akita, Ch. Kimdamar's Jumbalaya Jazz (call name "JJ").
Susan Thorpe-Vargas has a doctorate in immunology and has an extensive chemistry and lab background. She has been involved in numerous Environmental Protection Agency cleanup sites. Susan also raises and shows Samoyeds.
1. Acupuncture was first discovered in China between 2696 BC and 2598 BC by Huang Di, "The Yellow Emperor," who was the third great emperor of China. Acupuncture was initiated and discovered during the Yellow Emperor's reign, and the surviving document is the "Yellow Emperor's Classic of Internal Medicine," translation by Ilza Veith, University of California Press, Berkeley, Calif. 1993. This Yellow Emperor's classic text is the basis for acupuncture and was the current book of medical care in the 2600s BC.
2. Author unknown, Huang Ti Nei Ching, "Yellow Emperor's Classic of Internal Medicine," published between 400 BC and 200 BC.
3. Boston Medical and Surgical Journal, Vol. 15, No. 6, September 14, 1836, p. 87.
4. S.J. Harveill, Les Secrets de la Medicine des Chinois, Consitant et al., Parfaite Connoissance du Pauls, 1671.
5. Sir William Osler, The Principles and Practice of Medicine, Appleton, N.Y., 1893.
6. Sheldon Altman, "Small Animal Acupuncture: Scientific Basis and Clinical Applications," in Allen M. Schoen and Susan G. Wynn (eds.), Complementary and Alternative Veterinary Medicine: Principles and Practice, Mosby, St. Louis, 1998, p. 147.
7. Harriet Beinfield and Efrem Korngold, Between Heaven and Earth, Ballantine, New York, 1991.
8. M. Sanchez-Araujo and A. Puchi, "Acupuncture Enhances the Efficacy of Antibiotics Treatment for Canine Otitis Crises," Acupuncture and Electrotherapy Research, Vol. 22, March-April 1997, pp. 191-206.
9. F.W. Smith Jr., "Acupuncture for Cardiovascular Disorders," Problems in Veterinary Medicine, Vol. 4, No. 1, March 1992, pp. 125-131.
10. C. Schwartz, "Chronic Respiratory Conditions and Acupuncture Therapy," Problems in Veterinary Medicine, Vol. 4, No. 1, March 1992, pp. 136-143.
11. K.C. Waters, "Acupuncture for Dermatologic Disorders," Problems in Veterinary Medicine, Vol. 4, No. 1, March 1992, pp. 194-199.
12. S.G. Dill, "Acupuncture for Gastrointestinal Disorders," Problems in Veterinary Medicine, Vol. 4, No. 1, March 1992, pp. 144-154.
13. J.H. Lin and R. Panzer, "Acupuncture for Reproductive Disorders," Problems in Veterinary Medicine, Vol. 4, No. 1, March 1992, pp. 155-161.
14. P.A. Rogers, A.M. Shoen, and J. Limehouse, "Acupuncture for Immune-Mediated Disorders: Literature Review and Clinical Applications," Problems in Veterinary Medicine, Vol. 4, No. 1, March 1992, pp. 162-193.
15. Lin and Panzer.
16. A.M. Schoen, "Acupuncture for Musculoskeletal Disorders," in A.M. Schoen (ed.), Veterinary Acupuncture: Ancient Art of Modern Medicine," Mosby, St. Louis, 1994, pp. 159-170.
17. R. Joseph, "Neurologic Evaluation and its Relation to Acupuncture: Acupuncture for Neurologic Disorders," Problems in Veterinary Medicine, Vol. 4, No. 1, March 1992, pp. 98-106.
18. Lin and Panzer.
19. L.A. Janssens, "Acupuncture for the Treatment of Thoracolumbar and Cervical Disc Disease in the Dog," Problems in Veterinary Medicine, Vol. 4, No. 1, March 1992, pp. 107-116.
20. T.E. Durkes, "Gold Bead Implants," Problems in Veterinary Medicine, Vol. 4, No. 1, March 1992, pp. 207-211.
21. Altman, p. 155.
22. A.M. Klide and S.H. Kung, Veterinary Acupuncture, University of Pennsylvania, Philadelphia, 1997.
23. A.M. Schoen (ed.), Veterinary Acupuncture: Ancient Art of Modern Medicine, Mosby, St. Louis, 1994.
24. Cheryl Schwartz, Four Paws, Five Directions, Celestial Arts, Berkeley, Calif., 1996,
25. "The Neurophysiologic Basis of Acupuncture," in Allen M. Schoen (ed.), Veterinary Acupuncture: Ancient Art of Modern Medicine, Mosby, St. Louis, 1994, pp. 36-38.
26. Altman, p. 156.
29. Stanton A. Glantz, Primer of Biostatistics, 4th ed., McGraw-Hill, New York, 1996.
30. Arthur Taub, "Nonsense with Needles," in Stephen Barrett, M.D., and William Jarvis, Ph.D., (eds.), The Health Robbers: A Close Look at Quackery in America, Prometheus Books, Amherst, N.Y., 1993. Excerpt available online at www.seanet.com/~vettf/Primer.htm.
31. Personal communication, John Pollack, Ph.D., Cornell University, Ithaca, N.Y., May 1999.