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1. The action of thiamine and related compounds on the isolated heart of clam (Meretrix meretrix lusoria) was investigated.2. S-benzoylthiamine (SBT) and thiamine propyl disulfide (TPD) among these related compounds displayed a very remarkable positive inotropic action, whereas thiamine, acetylthiamine, thiamine diphosphate, thiamine triphosphate, benzoylthiamine monophosphate and ATP did not practically display any clear action.3. SBT and TPD showed a remarkable antagonistic action against the negative inotropic action of acetylcholine, but have no effect on the action of 5-hydroxytryptamine.4. The positive inotropic action of SBT and TPD was retained in K-free medium, but it completely disappeared in Na-free or Cafree medium. When more or less Na+ or Ca2+ was present in the medium, the action of SBT and TPD appeared as in the normal medium.5. The positive inotropic action of SBT and TPD, therefore, is believed to be closely related to the transport system of the cellular membrane of the clam heart muscle, in which Na+ and Ca2+ are involved.

Non-heat-coagulable protein was isolated from muscle extracts of Meretrix meretrix, Mactra sulcataria, and Atrina Japonicum, respectively. Content of this proteinous material in muscle as well as contents of nitrogen and reducing substance in the material was estimated (Table 1). The paper-electrophoretic analysis revealed that the material consisted at least of three subfractions with different mobilities. From these three, one having zero mobility was precipitated with acetic acid. It was found furthermore that the heat-coagulable components of muscle extracted with a buffer solution of low ionic strength (μ=0.1, pH 7.8)turned noncoagulable when dialyzed for short time (about 3 hours) against the same buffer solution as the above extractant. Whereas the paper-electrophoretic behaviours remained unchanged after such dialysis, the coagulability of these comppnents changed to a high degree. These non-coagulable matters were found to be of low mobility, while the coagulated porteins showed no mobility as expected. Molecular event leading to the said loss of coagulability is not clear as yet, though the loss seems to be connected mcre or less intimately with pH of the dialysate.

1. 1. An adenosine aminohydrolase was extracted from the mid-gut gland of the clam, Meretrix meretrix lusoria (Gmelin), in a highly purified form which, though heat-labile, could be stored over a month at 0°C without losing the specific activity amounting to 750-fold. 2. 2. The preparation catalysed the reaction of the first order, with the activation energy of 14,600 cal under the experimental conditions, showing the velocity constant of 13·18 × 10 −2 min −1 . 3. 3. A sharp optimum was found at pH 5·0. The Michaelis-Menten constant was 6·9 × 10 −5 M at 26°C at the optimal pH. 4. 4. This enzyme specifically decomposes adenosine and deoxyadenosine. Mercury, either metallic or organic, and fluoride inhibit the enzymatic reaction, though many common agents are not foond effective.

1. 1. A precipitate of water-homogenized midgut gland was suspended in 3 M NaCl, heat-shocked (50°C, 5 min), dialyzed against 0·2 M NaCl and suspended in 3 M NaCl to obtain a preparation with 17·7-fold activity of dephosphorylating 5′-AMP. 2. 2. It decomposed 2′-, 3′- and 5′-AMP, 5′-dAMP, 5′-UMP, 5′-IMP, 5′-GMP, 5′-CMP, 5′-ADP, ATP, β-glycerophosphate and p- nitrophenyl phosphate at pH 8·8, but did not attack l -α-lecithin and sodium creatine phosphate.

1. 1. Phosphohydrolytic activity was studied in the homogenized mid-gut gland tissue, using nucleotides (5′-AMP, 3′-AMP, 5′-IMP and GMP) and β-glycerophosphate as substrates. 2. 2. For nucleotides there were two optima of pH (8·5–9·7, 4·0–4·2). For β-glycerophosphate the activity was restricted to the alkaline region (pH 9·5).

The present study aims to make contributions to our knowledge, now rather scanty, of various effects of chemicals in the medium on pisces and mollusca living in. Cyprinus carpio L., Anguilla japonica and Meretrix meretrix (L.), were kept in water in which various chemical substances were dissolved with varying concentrations, and their responses were observed. According to the degree of the responses, the chemical substances employed may be arranged in discending order as follows: metallic salts (such as cupper sulphate, zinc sulphate and lead nitrate), acids and alkalis (such as sulphuric acid, sulphurous acid, ammonia and sodium carbonate) and the others (neutral salts such as salts of alkali metals and alkali earth metals).

Chemical composition and some physicochemical properties were studied on the body fluid which flow out from the body of Meretrix meretrix, Paphia philippinarum and Mactra sulcataria when the shells were removed. Each the liquid taken from the shells given above containes no taurine but betaine, and three kinds of picrates were isolated from monoaminofraction. The picrate deeived from Paphia is identical with oxyproline picrate. The melting point of picrates from Meretrix and Mactra is 260-262°C, 260°C, and nitrogene content 17.1%, 20.8%, respectively. The melting point of benzoyl deriva ive of the matter taken out from the picrate of Mactra is 172-173°C, and ninhydrine reaction assumed a deep blue violet colour.

1. 1. F-actin was directly isolated from adductor muscle of the clam Meretrix meretrix by the method of Szent-Gyorgyi and his associates (1970). The purity of F-actin was approximately 20 per cent. The preparation contained a number of spherical particles of about 250 A in diameter. 2. 2. Clam F-actin was rather stable in 0·1 M KC1, pH 8·0 or in 0·04 M KC1, pH 6·0. 3. 3. Clam F-actin was very heterogeneous in particle length, the number-average length: 0·24 μ and the weight-average length: 1·07 /gm. 4. 4. Trypsin treatment resulted in an appreciable digestion of F-actin particles. F-actin became short in length by sonication, but the recovery of length after sonication was slow and incomplete.

The ciliary movement of the gills of Meretrix meretrix (LINNE) as studied by the method of NOMURA and TOMITA in sea water, with its density 1•0200 at 15C, is shown in Fig. 1. The maximum value 1.27cm/min was got at a temperature 25.5C. The movement in question was almost null at temperatures 1•5°C and 41°C.