Abstract: The debilic acid(C₁₈H₁₃O₇N)(Ⅰ)is a new component isolated from Aristolochia debilis,S.et Z.as reported in our previous communication(Ⅰ).It closely resembles to Aristolochic acid(Ⅱ)C₁₇H₁₁O₇N,both in chemical and physical properties,Decarboxylation of(Ⅰ)by means of copper powder in quinoline,gave a compound C₁₆H₁₁O₅N(Ⅳ),m.p.206°,which was identified as 1-methoxy-5,6-methylene dioxy-9-nitro-phenagthrene,It is also obtainable from(Ⅱ)by the similar method.Owing to the negative result of the Kohn-Roth's determination of(Ⅳ),it is believed that the excessive methylene group in(Ⅰ)is an acetic radial rather than carboxyl group linking in(Ⅱ).Assuming the carboxyl group in(Ⅰ)is vicinal to the nitro-group,a neutral lactam should be formed instead of a basic amino compound.A lactam has been isolated in the present work.This fact interprets that the acetic radical should be existed either at 8-or 10-position. On the other hand,from the viewpoint of biogenetics,Aristolochiaceae,in the cou rse of evolution,is a family similar to those of Papaveraceae and Magnoliaceae.The last two mentioned families are well-known in containing alkaloids with tetrahydroisoquinoline nucleus which,in majority,carried a methoxy or methvlene-dioxy groups between 6-& 7-position. From the above facts and together with the strcture of aristolochic acid,the anthors suggest that the biosynthetic relationships between the aristolochic acid(including its related compounds)and aporphine series are as follows: If so,the acetic radical is more suitable in the 8-position than in the 10-position.In order to clarify the mutual relationship between the acidic and basic components,the alkaloid part which isolated from A.debilis,was subjected to selenium dehydrogenation.A crystalline substance m.p.240-41°was obtained. From its UV-spectra it was identified as an analogue of 1-ethyl-phenanthrene which can be obtained from aporphine nuclea as a hydrocarbon. In consequence,the authors recommend the following tentative formula for the debilic aeid:-