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Notes: Summary 1. Methane fermentation of Ca-acetate is about as sensitive to phenylhydrazine, hydroxylamine and azide as it is to sulphite (inhibition by 10−2 m 70, 83, 94 and 95 % resp.; by 10−3 m 0, 39, 49 and 31 % resp.). 2. The sensitivity to dimedone is much less, 10−2 m inhibiting 17% only. 3. The process is much more sensitive to cyanide, 5.10−4 m giving already ±90% inhibition. 4. The sensitivity to sulphide is much less, as 5.10−2 m is necessary for complete inhibition, whereas 10−2 m does not inhibit at all. 5. Cultures of methane bacteria on Ca-acetate can be accustomed to 0.15 % formaldehyde which is fermented to CH4 and CO2 in presumably equimolecular proportions. 6. The results are discussed in the light of data on the action of these toxic substances in biological systems in general, with special reference to anaerobic bacteria.

Notes: Summary 1. The purple sulphur bacteria are able to develop in media containing only one simple, nitrogen-free organic compound, in the absence of oxidizable sulphur compounds. 2. Radiant energy is indispensable for development in these media. 3. A quantitative chemical investigation has been carried out of the metabolism in cultures containing lactate, pyruvate, acetate, succinate, malate or butyrate as the organic substrate. 4. In these cultures practically no metabolic products other than relatively small amounts of CO2 have been detected; in the butyrate cultures CO2 is taken up instead of being formed. 5. By determining the carbon content of the bacterial substance synthesized in the cultures, it has been shown that in all probability the substrate is completely converted into cell material and CO2, i. o. w. that the assimilation predominates in the metabolism. 6. The differences in the amount of CO2 formed (or taken up) per unit of substrate consumed in cultures with different substrates are caused by the different oxidation values of the various substrates, the average oxidation value of the cell material of the bacteria being approximately the same with all substrates. 7. Since a consideration of assimilation in general leads to the insight that the greater majority of organic cell constituents is formed from the substrate via pyruvic acid, the ways in which this acid can be formed from the various substrates used in the experiments have been discussed. 8. The conversion of the substrate into pyruvic acid involves one or more dehydrogenations; a consideration of the hydrogen acceptors which may effect this dehydrogenation shows that CO2 must play a prominent part as an acceptor in this process. 9. In connection with point 2 this leads to the conclusion that photosynthetic processes are involved in the metabolism of the purple sulphur bacteria in organic media. 10. In the equation for photosynthesis in general: $${\text{CO}}_{\text{2}} {\text{ + }} {\text{2H}}_{\text{2}} {\text{A}} \to {\text{CH}}_{\text{2}} {\text{O}} {\text{ + }} {\text{2A}} {\text{ + }} {\text{H}}_{\text{2}} {\text{O}}$$ H2A may now be replaced by organic substances as well as by H2S or H2O.

Notes: Summary The relationships among three methods for evaluating texture (sloughing during cooking, hardness of cooked potato dice and shear press value of French fries) and some chemical constituents (Ca, Mg, K, free pectin, phytin and citrate) were investigated, using the main specific gravity classes of seven Dutch potato varieties. The interplay of these constitutents (except K) in the softening of the texture during cooking was expressed as follows: Only the shear press value showed a relationship with the specific gravity. None of the textural-properties was geverned by the PC PMC number or by water uptake of raw slices. The same properties were determined after 50 and 100 days storage at 10 and 4 C. A decrease in sloughing and hardness, but an increase in shear press value occurred. PCMPC number also increased, but remained quite low, explaining its lack of influence on texture.

Notes: Summary 1. Cereal straw was partially hydrolyzed with dilute sulphuric or hydrochloric acid at elevated temperatures, yielding about 20% of matter assimilable byTorulopsis utilis (calculated on oven-dry straw), which consisted chiefly of xylose, with small amounts of glucose and acetic acid. 2. Experiments on a laboratory scale with non-fermentable substrates like ethanol and acetic acid showed that also in these cases an ample aeration is an essential condition for a good yield. 3. Acetic acid is harmful to the yeast, even in small concentrations, when the pH is lower than 5.0. 4. Small quantities of glucose or acetic acid stimulate the conversion of xylose byTorulopsis utilis. 5. With an adequate aeration and an initial pH of 5.5–6.0 (maintained at this level until the acetic acid has disappeared and then lowered to 4.0–4.5) satisfactory conversion rates and yields could be obtained on straw extracts as mentioned sub 1. 6. The results of the laboratory experiments mentioned sub 5 could be reproduced in a semi-technical installation with a capacity of 200 l straw extract. 7. Good results were obtained in this installation with aVogelbusch aeration device, while foaming could be adequately controlled by means of a rotating wire screen.

Notes: Summary It has been proved that methane fermentation of sodium and calcium acetates is strongly inhibited by both sodium and calcium sulphites. In the region of optimum pH of this fermentation (pH 6.0 to 6.5) a concentration of 0.003 to 0.01 % sodium sulphite is enough to produce perceptible inhibition. At a concentration of 0.1 % Na2SO3 methane fermentation was inhibited completely for some days. Hereafter a recovery took place, most probably due to the development of micro-organisms converting sulphites to H2S. At a pH higher than 6.5 methane fermentation was less sensitive to Na2SO3 and CaSO3.