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Observation of the tongue is one of the components of the five senses in TCM. However, its content is very rich and has developed into a specialized tongue diagnosis, thus warranting a separate section for explanation.
Tongue diagnosis primarily focuses on the observation of the tongue, and also includes inquiries about tongue sensation (taste) and palpation methods. Tongue observation is a diagnostic method that involves examining the tongue’s appearance. The tongue’s appearance is composed of the color and shape of the tongue body and the tongue coating.
Therefore, tongue observation mainly involves examining the tongue body and the tongue coating.
(1) The Relationship Between the Tongue and the Internal Organs and Meridians
The connection between the tongue and the internal organs is primarily realized through the pathways of the meridians. According to the “Nei Jing,” the heart, liver, spleen, kidneys, and bladder, as well as the San Jiao, stomach, and other organs, are directly connected to the tongue through the meridians, collaterals, or sinews. As for the lungs, small intestine, large intestine, and gallbladder, although there is no direct connection to the tongue, they are paired with the hand and foot Taiyin, hand and foot Yangming, and hand and foot Shaoyang, thus the meridian qi of the lungs, small intestine, gallbladder, and large intestine can also indirectly connect to the tongue. Therefore, the tongue is not only the orifice of the heart but also an external manifestation of the spleen, and it reflects the conditions of the five internal organs and six bowels. Physiologically, the essence and qi of the internal organs can reach the tongue through the meridians, nourishing the tongue and maintaining its normal functional activities. Pathologically, changes in the internal organs must also affect the essence and qi, which will be reflected on the tongue.
From the perspective of biological holography, any part resembles a miniature of the whole, and the tongue is no exception. Hence, it has been said that the tongue corresponds to the locations of the internal organs. The basic rule is: the upper part corresponds to the upper organs, the middle part corresponds to the right organs, and the lower part corresponds to the lower organs. The specific classification methods are as follows:
1. Diagnosis of tongue parts based on the internal organs
The heart and lungs are located at the top, thus the tip of the tongue corresponds to the heart and lungs; the spleen and stomach are in the middle, hence the middle part of the tongue corresponds to the spleen and stomach; the kidneys are located at the bottom, thus the root of the tongue corresponds to the kidneys; the liver and gallbladder are located on the sides of the body, thus the sides of the tongue correspond to the liver and gallbladder, with the left side corresponding to the liver and the right side corresponding to the gallbladder. This method is generally used for diagnosing internal injuries and miscellaneous diseases.
2. Diagnosis of tongue parts based on the San Jiao
The tongue parts are classified according to the upper, middle, and lower positions of the San Jiao, with the tip of the tongue corresponding to the upper Jiao, the middle part corresponding to the middle Jiao, and the root corresponding to the lower Jiao. This classification is often used for external pathogenic changes.
3. Diagnosis of tongue parts based on the stomach
The tip of the tongue corresponds to the upper abdomen, the middle part corresponds to the middle abdomen, and the root corresponds to the lower abdomen. This classification is commonly used for gastrointestinal diseases.
Using the various parts of the tongue to correspond to the internal organs is one of the current research topics in biological holography. Although there are different opinions, they all have reference value. In clinical diagnosis, it is essential to combine the examination of the tongue body and coating for verification, but all four diagnostic methods should be considered for a comprehensive judgment, and one should not be overly mechanical.
(2) The Content of Tongue Observation
The content of tongue observation can be divided into two parts: the tongue body and the tongue coating. The tongue body, also known as the tongue substance, consists of the muscle and vascular tissues of the tongue. The observation of the tongue body can be further divided into four aspects: spirit, color, shape, and state. The tongue coating is a layer of coating attached to the tongue body, and the observation of the tongue coating can be divided into two aspects: the color and quality of the coating.
The normal tongue appearance is referred to as “pale red tongue with thin white coating.” Specifically, the tongue body is soft, moves flexibly, and has a pale red color that is bright and vivid; its size is moderate, without any abnormal shape; the tongue coating is thin, white, and moist, with evenly distributed granules, lightly covering the tongue surface, and cannot be wiped off, as it is rooted and integrated with the tongue body, with moderate moisture, neither sticky nor greasy. In summary, the normal tongue appearance is a comprehensive representation of the normal manifestations of the tongue body and coating.
1. Observation of the Tongue Body
(1) Tongue Spirit: The tongue spirit is primarily reflected in the luster and vitality of the tongue body. The key to observing the tongue spirit lies in distinguishing between vitality and dullness.
Vitality refers to a moist and radiant appearance, characterized by flexible movement, a bright and vivid tongue color, and a lively spirit, indicating a good prognosis even in illness. Dullness refers to a dry and lackluster appearance, characterized by inflexible movement, a dry and dark tongue body, indicating a poor prognosis. Thus, the presence or absence of tongue spirit reflects the condition of the internal organs, qi and blood, and body fluids, which is related to the prognosis of the disease.
(2) Tongue Color: This refers to the color of the tongue body. Generally, it can be classified into pale white, pale red, red, crimson, purple, and blue. Except for pale red, which is the normal tongue color, the others indicate pathological conditions.
① Pale Red Tongue: The tongue color is pale red, neither too deep nor too shallow, indicating sufficient heart qi and yang qi, thus representing a normal tongue color.
② Pale White Tongue: The tongue color is lighter than that of the pale red tongue, even lacking blood color, referred to as pale white tongue. This indicates a deficiency of yang and a weakened ability to generate blood, leading to a pale tongue color. Therefore, this tongue indicates deficiency cold or dual deficiency of qi and blood.
③ Red Tongue: The tongue color is bright red, deeper than the pale red tongue, indicating a heat condition. This can be seen in excess conditions or deficiency heat conditions.
④ Crimson Tongue: Crimson refers to a deep red tongue, darker than the red tongue. This indicates different diseases, with external pathogens causing heat in the blood and internal injuries indicating yin deficiency and excess fire.
⑤ Purple Tongue: A purple tongue is generally caused by poor blood circulation and stagnation. Thus, a purple tongue indicates a disease related to cold and heat. Excess heat can cause dryness and stagnation, often appearing as crimson and dry. Cold can cause blood stasis or yang deficiency leading to a pale purple or blue tongue that is moist.
⑥ Blue Tongue: The tongue color resembles exposed “blue veins,” with no red color, referred to as blue tongue, described in ancient texts as resembling a water buffalo’s tongue. This indicates excess cold and stagnant yang, or yang deficiency with cold accumulation, or internal blood stasis.
(3) Tongue Shape: This refers to the shape of the tongue body, including aging, thickness, swelling, cracks, prickles, and tooth marks.
① Old Tongue: The tongue body has rough texture and a firm appearance, referred to as an old tongue. Regardless of the tongue color or coating, an old tongue indicates an excess condition.
② Tender Tongue: The tongue body has a delicate texture, a tender color, and is often swollen, referred to as a tender tongue, indicating a deficiency condition.
③ Swollen Tongue: This can be classified into thick and swollen. A tongue that is larger than normal, even extending to fill the mouth, or has tooth marks, is referred to as a thick tongue. A tongue that is swollen and cannot retract or close the mouth is referred to as a swollen tongue, often caused by water retention or phlegm dampness. A swollen tongue is often due to heat toxins or alcohol toxins causing qi and blood stagnation, indicating a heat condition or toxic disease.
④ Thin Tongue: A tongue that is small and thin is referred to as a thin tongue. This is generally due to insufficient qi, blood, or body fluids, leading to an undernourished tongue body. This indicates dual deficiency of qi and blood or excess fire due to yin deficiency.
⑤ Prickly Tongue: The surface of the tongue has soft prickles (i.e., lingual papillae), which is normal. If the soft prickles on the tongue surface enlarge and protrude like spikes, it is referred to as a prickly tongue. This is often due to excessive heat. The more prickles, the more severe the heat. The location of the prickles can help differentiate the heat in the internal organs, such as prickles on the tip indicating excessive heart fire; prickles on the sides indicating excessive liver and gallbladder fire; prickles in the middle indicating excessive stomach and intestinal heat.
⑥ Cracked Tongue: A tongue with cracks that are not covered by coating is referred to as a cracked tongue. This is often due to deficiency of essence and blood, leading to insufficient nourishment of the tongue body. Thus, it often indicates deficiency of essence and blood. Additionally, about 0.5% of healthy individuals have deep longitudinal and transverse grooves on the tongue, referred to as congenital tongue fissures, which are covered with coating and do not indicate any discomfort, differing from cracked tongues.
⑦ Tooth-marked Tongue: A tongue with indentations along the edges from teeth is referred to as a tooth-marked tongue. This is often due to spleen deficiency leading to an inability to transform water and dampness, causing obstruction in the tongue and resulting in a swollen tongue that is pressed by the teeth. Therefore, a tooth-marked tongue is often seen with a swollen tongue, indicating spleen deficiency or excess dampness.
(4) Tongue State: This refers to the state of the tongue during movement. A normal tongue state is characterized by sensitive movement, while pathological states may include rigidity, weakness, elongation, shortening, numbness, trembling, deviation, and protrusion.
① Rigid Tongue: A tongue that is stiff and rigid, with limited movement, leading to unclear speech, is referred to as a rigid tongue. This is often due to heat disturbing the heart spirit, or high fever damaging yin, or phlegm obstructing the tongue. This is often seen in conditions of heat entering the pericardium, high fever damaging body fluids, phlegm obstructing the tongue, stroke, or stroke precursors.
② Weak Tongue: A tongue that is weak and lacks strength to extend or retract is referred to as a weak tongue. This is often due to extreme deficiency of qi and blood, leading to insufficient nourishment of the muscles. This can be seen in conditions of dual deficiency of qi and blood, extreme heat damaging body fluids, or extreme yin deficiency.
③ Elongated Tongue: A tongue that extends outside the mouth with difficulty retracting is referred to as an elongated tongue. This is often due to relaxation of the tongue muscles. This can be seen in conditions of internal excess heat, phlegm fire disturbing the heart, or qi deficiency.
④ Shortened Tongue: A tongue that is contracted and cannot extend is referred to as a shortened tongue. This can be due to cold constricting the muscles, internal obstruction of phlegm dampness, or excessive heat damaging body fluids, leading to contraction of the tongue. Regardless of whether it is due to deficiency or excess, it indicates a critical condition.
⑤ Numb Tongue: A tongue that feels numb and lacks movement is referred to as a numb tongue. This is often due to the inability of the nourishing blood to reach the tongue. If the numbness occurs without reason and is intermittent, it indicates heart blood deficiency; if the numbness is accompanied by trembling or stroke symptoms, it indicates internal wind.
⑥ Trembling Tongue: A tongue that trembles uncontrollably is referred to as a trembling tongue. This is often due to dual deficiency of qi and blood, leading to insufficient nourishment or extreme heat damaging body fluids, resulting in wind. This can be seen in conditions of blood deficiency leading to wind or extreme heat leading to wind.
⑦ Deviated Tongue: A tongue that extends to one side is referred to as a deviated tongue. This is often due to wind obstructing the meridians or phlegm wind obstructing the meridians, but it can also be due to wind affecting the internal organs, leading to relaxation of the tongue muscles on the affected side. This is often seen in stroke conditions or stroke precursors.
⑧ Protruding Tongue: A tongue that frequently extends outside the mouth is referred to as a protruding tongue; a tongue that licks the lips or moves in and out quickly is referred to as a moving tongue. Both are referred to as protruding tongues, often due to heat in the heart and spleen meridians damaging body fluids, leading to frequent movement. Protruding tongues are often seen in children with developmental delays.
2. Observation of the Tongue Coating
The normal tongue coating is produced by the upward steaming of stomach qi, thus the changes in stomach qi can be reflected in the tongue coating. The formation of pathological tongue coating can be due to the upward rise of turbid qi from food stagnation or the rise of pathogenic qi. When observing the tongue coating, attention should be paid to both the quality and color of the coating.
(1) Coating Quality: This refers to the thickness, moisture, roughness, stickiness, decay, peeling, and whether it has roots or not.
① Thickness: Thickness is classified as “visible base” and “not visible base.” If the tongue coating is thin enough to see the tongue body, it is referred to as thin coating. This is produced by stomach qi and is considered normal. If seen in disease, it often indicates the early stage of illness or that the pathogenic factor is still superficial. If the tongue coating is thick enough that the tongue body cannot be seen, it is referred to as thick coating. This often indicates that the pathogenic factor has entered the interior or that there is food stagnation, indicating a more severe condition. If the coating changes from thin to thick, it often indicates that the righteous qi is unable to overcome the pathogenic factor, and the condition is worsening; if the coating changes from thick to thin, it often indicates that the righteous qi is recovering, and the internal pathogenic factor is dissipating, indicating improvement in the condition.
② Moisture: A moist tongue surface with moderate dryness is referred to as moist coating, indicating that body fluids are not damaged. If there is excessive moisture, the coating is slippery and may even lead to drooling, indicating slippery coating. This reflects the presence of dampness and cold, often seen in conditions of yang deficiency with phlegm and water retention. If the coating appears dry and rough, it is referred to as dry coating, indicating that body fluids are unable to ascend. This is often seen in conditions of excessive heat damaging body fluids, insufficient yin, or yang deficiency leading to water not transforming into body fluids, or dryness damaging the lungs. If the coating changes from moist to dry, it often indicates that the drying pathogenic factor is damaging body fluids, or that excessive heat is consuming body fluids, indicating worsening of the condition; if the coating changes from dry to moist, it often indicates that the drying heat is receding and body fluids are recovering, indicating improvement in the condition.
③ Decayed Coating: A thick coating with large, loose granules resembling tofu dregs on the tongue surface, which can be wiped off, is referred to as decayed coating. This is due to excess yang heat in the body, causing turbid qi in the stomach to rise. This is often seen in phlegm dampness or food stagnation, and may indicate heat in the stomach and intestines. A coating that is fine and dense, which cannot be wiped off, and is covered with a layer of sticky liquid, is referred to as sticky coating. This often indicates that the spleen is unable to transport and transform, leading to internal dampness and stagnation, often seen in phlegm dampness conditions.
④ Peeling Coating: If the tongue has coating that suddenly peels off completely or partially, revealing the base, it is referred to as peeling coating. If the entire coating peels off without regrowth, leaving a smooth surface, it is referred to as mirror tongue or smooth tongue. This is due to exhaustion of stomach yin and severe damage to stomach qi, indicating a critical condition. If the coating peels off partially, leaving some remnants, it is referred to as mottled peeling coating, indicating damage to both stomach qi and yin. The change from having coating to none indicates insufficient stomach qi and yin, and declining righteous qi; however, if a thin white coating regrows after peeling, it indicates that the pathogenic factor has been expelled and the righteous qi is recovering, which is a good sign. It is important to note that whether the coating increases or decreases, it should gradually change; if the coating changes suddenly, it often indicates a rapid change in the condition.
⑤ Coating with Roots vs. Coating without Roots: Regardless of thickness, if the coating is firmly attached to the tongue surface, appearing as if it grows from the tongue, it is referred to as coating with roots, also known as true coating; if the coating is not firmly attached and can be easily scraped off, it is referred to as coating without roots, also known as false coating. Coating with roots indicates that the pathogenic factor is strong but the stomach qi is not yet weakened; coating without roots indicates that the stomach qi has weakened.
In summary, observing the thickness of the tongue coating can indicate the depth of the disease; the moisture of the coating can indicate the balance of body fluids; the decayed coating can indicate dampness and turbidity; the peeling coating and the presence or absence of roots can indicate the changes in qi and yin and the trend of the disease.
(2) Coating Color: This refers to the color of the tongue coating. Generally, it can be classified into white, yellow, gray, and black, along with variations. The color of the coating is related to the nature of the pathogenic factor. Therefore, observing the coating color can help understand the nature of the disease.
① White Coating: This is commonly seen in exterior conditions and cold conditions. If the external pathogenic factor has not yet penetrated the interior, the tongue coating often remains unchanged, still appearing as normal thin white coating. If the tongue is pale with a moist white coating, it often indicates interior cold or cold dampness. However, in special cases, white coating can also indicate heat conditions. For example, if the tongue is covered with thick white coating resembling a pile of white powder, which feels moist, it is referred to as “accumulated powder coating,” indicating the presence of external pathogenic factors or internal heat. This is often seen in warm epidemics or internal abscesses. Additionally, if the coating is white, dry, and cracked like sand, it is referred to as “rough cracked coating,” indicating rapid transformation of dampness into heat, leading to internal heat rising quickly, often seen in warm diseases or improper use of warming herbs.
② Yellow Coating: This generally indicates interior conditions and heat conditions. Due to heat pathogens, the coating appears yellow. Light yellow indicates mild heat, deep yellow indicates severe heat, and burnt yellow indicates heat with obstruction. In external diseases, if the coating changes from white to yellow, it indicates that the exterior pathogenic factor has penetrated the interior and transformed into heat. If the coating is thin and light yellow, it indicates exterior wind-heat or wind-cold transforming into heat. If the tongue is pale and swollen with a yellow, slippery coating, it often indicates yang deficiency with water dampness.
③ Gray Coating: Gray coating is a light black color. It often develops from white coating or can be seen alongside yellow coating. It generally indicates interior conditions, often seen in interior heat conditions, but can also be seen in cold-warm conditions. A dry gray coating often indicates excessive heat damaging body fluids, which can be seen in external heat diseases or internal injuries.
④ Black Coating: Black coating often develops from burnt yellow or gray coating. Generally speaking, regardless of whether it is cold or heat, it often indicates a critical condition.
The darker the coating, the more severe the condition. For example, if the coating is black and dry, it may even have prickles, indicating extreme heat and dryness; if the coating is black and dry, it may indicate intestinal dryness and constipation, or impending stomach failure; if it is seen at the root of the tongue, it indicates severe heat in the lower Jiao; if it is seen at the tip of the tongue, it indicates self-burning heart fire; if the coating is black and moist, with a pale tongue, it indicates internal excess cold and water dampness; if the coating is black and sticky, it indicates phlegm dampness obstruction.
3. Comprehensive Examination of the Tongue Body and Coating
The development of a disease is a complex and holistic process. Therefore, while understanding the basic changes in the tongue body and coating and their associated diseases, it is also essential to analyze the interrelationship between the tongue body and coating. Generally, it is believed that observing the tongue body focuses on distinguishing the strength of the righteous qi, which also includes the nature of the pathogenic qi; observing the tongue coating focuses on distinguishing the depth and nature of the pathogenic qi, which also includes the existence of stomach qi. In terms of their relationship, both must be considered for a comprehensive understanding. In general, the changes in the tongue body and coating are consistent, and their associated diseases often represent a comprehensive picture of their respective diseases. For example, in cases of internal excess heat, the tongue is often red with a yellow and dry coating; in cases of internal deficiency cold, the tongue is often pale with a white and moist coating. This is the key to mastering the complexities of tongue diagnosis. However, there are also instances where the changes are inconsistent, thus requiring a comprehensive assessment of all four diagnostic methods. For example, a white tongue may indicate cold or dampness, but if accompanied by a red tongue and dry white coating, it indicates dryness and heat damaging body fluids, as the drying heat transforms quickly, leading to a change in the coating color before it turns yellow. Similarly, a thick white coating may indicate excessive heat, but it does not indicate cold; gray or black coatings can indicate heat or cold, and must be distinguished based on the moisture of the tongue body. Sometimes, the associated diseases may seem contradictory, but they must be viewed together. For example, a red tongue with a white, slippery coating may indicate heat in the nutrient level and dampness in the qi level in external conditions; in internal injuries, it may indicate excess fire due to yin deficiency, along with phlegm dampness and food stagnation. Thus, while learning, one can grasp the distinctions, but in practice, a comprehensive examination is essential.
(3) Methods and Precautions for Tongue Observation
To obtain accurate results in tongue observation, it is essential to pay attention to methods and certain issues, which are described as follows:
1. Tongue Extension Position: During tongue observation, the patient should extend their tongue outside the mouth to fully expose the tongue body. The mouth should be opened as much as possible, and the tongue should be relaxed without force, with the tongue surface flat and extended, and the tip naturally hanging towards the lower lip.
2. Sequence: Tongue observation should follow a certain sequence, generally starting with the tongue coating, followed by the tongue body, in the order of the tip, sides, middle, and root of the tongue.
3. Lighting: Tongue observation should be conducted in sufficient and soft natural light, facing a bright area to allow light to shine directly into the mouth. Avoid colored doors and windows and surrounding reflective colored objects to prevent false impressions of the tongue coating color.
4. Diet: Diet can significantly affect the tongue appearance, often causing changes in the shape and color of the tongue coating. Chewing food can cause thick coatings to become thin; drinking water can moisten the tongue surface; excessively cold, hot, or spicy foods can change the tongue color. Additionally, certain foods or medications can stain the tongue coating, creating false impressions, referred to as “dyed coating.” These are temporary and do not reflect the essence of the disease. Therefore, in clinical practice, if the tongue coating does not match the condition or if there are sudden changes in the coating, it is essential to inquire about the patient’s recent diet, especially in the period leading up to the consultation.
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