On the other hand, pachyman2, obtained from Poria cocos Wolf (Bukuryo) and hitherto considered to be a b (13) linear glucan, is completely devoid of antitumour activity. Re-examination of the structure of pachyman has demonstrated, however, that the b (13) chain has some b (16)-linked branches. The gas chromatogram (0.75 per cent 'SE-30' on 'Gas-Chrom Q? 6 feet 0.25 inch, 230 C) of the disaccharide portion, the product of partial acetolysis of pachyman, exhibited the peak for gentiobiose octaacetate, thus indicating the presence of b (16)-glycoside linkages, besides that of laminaribiose octaacetate indicative of b (13) glycoside linkages. The results of periodate oxidation and Smith degradation3,4 also supported the presence of b (16) linkages. Fig. 1. Chemical conversion of pachyman to its oxidized/reduced derivative (II) and the final product of mild hydrolysis (III).Experiments were carried out to sever the b (16) linkages in pachyman by the method shown in Fig. 1 to convert it to a lentinan-like b (13) linear glucan. By this conversion, a new polysaccharide with a strong antitumour activity was formed, A suspension of 3.7 g of pachyman in 450 ml. water was mixed with 150 ml. aqueous solution of 0.1 M sodium metaperiodate and stirred for 40 h in darkness at room temperature. The mixture was adjusted to pH. 4.5 with acetic acid and centrifuged to yield a colourless paste (I). This substance was suspended in 200 ml. of water, and a solution of 800 mg of sodium borohydride in 100 ml. water was added with stirring; the mixture was stirred for 20 h to effect reduction. A further 300 mg of sodium borohydride was added and the stirring continued for another 20 h. The reaction mixture was adjusted to pH. 6.0 with acetic acid and centrifuged, and the precipitate was collected, washed with ethanol and ether, and dried to 3 g of white powder (II). This product was suspended in 200 ml. of 0.05 M sulphuric acid and stirred vigorously at room temperature for 24 h to effect mild hydrolysis. The mixture was centrifuged and the precipitate was washed consecutively with water, ethanol and ether, and dried to give 2.87 g of antitumour polysaccharide (III) having an optical rotation [a]2D + 23.3 (c=1, 1 M NaOH). This substance was insoluble in water but readily dissolved in alkalis, and has marked swelling properties. Its infrared spectrum lacked any absorptions corresponding to aldehyde or carboxyl groups. Table Sample>1. ANTITUMOU Dose R EFFECT 0Body weight change t ?F PACHYJLA Average weight of umour (g) .N, II ANDInhibition ratio (per cent) III Complete regressionPachyman 5 mg/kg x 10 + 4-4 g 6-6 0 0/8 1 mg/kg x 10 + 5-9g 6-8 -3 0/9Control + 5-6 g 6-6 0/8 II 6 mg/kg x 10 + 2-3g 0-3 96 4/9Control + 0-9 g 6-7 0/8 III 5 mg/kg x 10 + 3-3 g 0-8 88 2/6Control + 0-9 g 6-7 0/8 Antitumour activity was tested by the method described previously1. A 7 day old ascites sarcoma 180 was transplanted subcutaneously into the right groin of a Swiss albino mouse. The test sample was injected intraperitoneally once a day for 10 days starting 24 h after transplantation. The mice were killed after 5 weeks, the tumours were extirpated and weighed, and inhibition ratios were calculated and compared with the findings in control mice. Complete regression of the tumours was recorded (Table 1). Although pachyman has no antitumour activity, derivatives II and III exhibited pronounced activity, similar to that manifested by lentinan (Table 1). Poriacocos Wolf is one of the most important crude drugs in Japan and in other Asian countries. Pachyman is extracted from this material in a yield of about 75 per cent. The yield of II and III from pachyman is about 80 per cent. The methods seem to be the simplest and most convenient for obtaining a polysaccharide with a marked antitumour activity against transplanted tumour. Neither II nor III has any toxicity. We propose calling III "pachymaran".The fact that such a marked difference in antitumour activity could result from a small change in fine structure, involving a small amount of b (16)-linked branching or some related structural difference arising from it, is of interest with respect to the biological activities of poly-saccharides in general. It is also of particular relevance to the question, raised in connexion with previous studies on antitumour polysaccharides, whether a minute amount of impurity might be the active principle. We are now studying the fine structure of pachyman, II and III, with a view to correlating structure with antitumour action in greater detail. We thank Dr Waro Nakahara for his encouragement, and Miss Reiko Tokuzen for her cooperation.