Abstract: 51 fresh adult cadavers of which 21 were male and 30 female, were randomly chosen, frozen and cut by anatomic sections after locating acupoints. Distances between the superficial dermal spots and dangerous deep spots at acupoints were measured after defrosting and the data obtained were statistically processed. Research pointed out an average dangerous depth of needling and proposed a safe depth of needling for 23 dangerous points on the chest.

A dangerous point is defined as an acupoint that can injure an organ by uncautious acupuncture of that point. There are about 23 dangerous points on the chest; (Ruzhong(S17)) of the Stomach Channel of Foot-Yangming is an acupoint to which acupuncture is forbidden and was not included in this research). Through the ages, different needling depths were recorded for these acupoints. Clinical doctors were worried about the vital organs such as the heart and the lung in the cavity of the chest. Our systematic research on these dangerous points aimed at providing the clinical doctors with a safe depth of needling to prevent accidents and improve acupuncture effects.

Materials and Methods
Materials: 51 fresh adult cadavers of which 21 were male and 3O female,were randomly chosen. 23 dangerous points on the chest were researched on the depth of needling: Shufu(KI27), Yuzhong(KI26), Shencang(KI25), Lingxu(KI24), Shenfeng(KI23), Bulang(KI22), Qupen(ST12), Qihu(ST13), Kufang(KT14), Wuyi(ST1), Yingchuang(ST16), Rugen(ST18), Qimen(Liv14), Riyue(GB24), Tianchi(PC1), Yuanye(GB22), Dabao(SP21), Zhejin(GB23), Zhourong(SP20), Xiongxiang(SP19), Tianxi(SP18), Shidou(SP17) and Tiantu(Ren22).

Methods: In accordance with the previous research method: first the acupoints were treated by drawing lines on the cadaver; then the cadavers were frozen by low temperature and 10 cut by acupoint sections for the measurement of the depths of the acupoints; finally the data obtained through these measurements were analyzed by computer statistical software.

Measurement Results
Of the 23 dangerous points on the chest, 22 are paired (left-right) and 1 is un-paired. The results of the measurements of these 22 dangerous paired ones, regardless of sex are: FootShufu(K27), Yuzhong(K26), Shencang(K25), Lingxu(K24), Shenfeng(K23)and Bulang (K22): the average depth of Shufu (K27) is the largest and the dangerous depth reaches about 26mm (This acupoint is near the sternoclavicular joint where the thoracic wall is thicker), the average dangerous depths of the other points are between 11.87 and 17.64mm and do not vary much. PEFOTS NEWS - March 2003, no. 3 • Pan European Federation of TCM Societies Among the points Quepen(S12), Qihu(S13), Kufang(K14), Wuyi(S15), Yingchuang(S16) and Rugen(S18), the distance of Quepen(S12) to the lung is the largest and the average depth reaches about 38mm.The superior part of the apex of the lung is more inside and there is a larger gradient from the apex of the lung to the lower and outer side, which results in a larger depth of Qupen(S12) to the lung. The depths of points Qihu(S13), Kufang(S14), Wuyi(S15), Yingchuang(16) and Rugen(S18) change gradually from large to small, from the upper side to the lower side. The depth of point Qihu(S13) is about 33.62mm and that of point Rugen(S18) is only about 12.21mm. Points Qimen(Liv14) and Riyue(G24) belong respectively to the Liver Meridian of Foot-Jueyin and the Gallbladder Meridian of Foot-ShaoYang and are on the same straight line with the Stomach Meridian of Foot-Yangming in an upward or downward direction. The thicknesses of these two points are similar to those of the adjacent points of the Stomach Meridian on the anterior chest wall. Points Zhourong(Sp20), Xiongxiang (Sp19), Tianxi(Sp18) and Shidou (Sp17) belong to the Spleen Meridian of Foot-Taiyin and the depths of these 4 points change from large to small from the upper to the lower side. The thickness of point Zhourong(Sp20) is about 24.7mm and that of point Shidou(Sp17) is about 15.17mm. This change is possibly related to the existence of the greater pectoral muscle and the smaller pectoral muscle. The thicknesses of points Yuanye(G22) and Zhejin(G23) of the Gallbladder Meridian of Foot-ShaoYang on the lateral chest wall under the axilla and point Dabao (Sp21) of the Spleen Meridian of Foot-Taiyin are close to the standard deviations of the 22 dangerous points on the chest that belong to the paired ones. That of point Quepen(S12) is largest(12.4mm), indicating that the dispersion degree of the dangerous point is larger in the samples and there is a larger difference among different individuals, and attention should be paid to the depth of needling. The significance test of the differences of the 22 paired dangerous points on the chest belonging to the paired ones show that the P value was in all cases larger than 0.05, indicating that there was no difference in the dangerous depth between the right and left side. The average dangerous depth of the unpaired dangerous point Tiantu(R22) on the chest is 22.91mm in the males and 21.59mm in the females, with standard deviation 7.97mm in the males and 7.17mm in the females. Significance test between the males and the females showed that the p value was larger than 0.05, indicating there was no difference between the males and the females.

Discussion
The means in the above table are the average depths from the skin to the dangerous spots. These average depths should never be reached in clinic, otherwise an acupuncture accident will take place. For the safety of acupuncture, we propose a range of depths of needling for dangerous points on the chest. The formula for calculating a safe depth is: an average dangerous depth x70%. The mean in the table was chosen as the average dangerous depth. Each point had two means in the right and left sides and the smaller one was taken as a standard. A safe depth of needling in this research is for medium-statue adults. As for very thin or fat persons treated in c1inic, it is suggested that the depth of needling should be adjusted for safety