1. succinic dehydrogenase of plant cells is not located on the outer cell membrane as was suggested for bacteria by Quastel. We have extended this work to red-beet tissue, which was stated by Bennet Clark and Bexon4 to be insensitive to malonate. We find that the effects of malonate on beet-tissue slices are closely similar to those recorded in Figs. 1 and 2 for carrot. There is one interesting difference. Malonic acid at pH4·0 causes inhibition of the cyanide-sensitive respiration13 of beet tissue, but (for well-washed tissue only) the rate of oxygen uptake later rises again to a value above the normal rate, after which there is once more a sharp decline. Simultaneously, the cells lose and oxidize some of their vacuolar pigment. We explain this additional complexity as due to the loss of cell organisation leading to non-respiratory oxidation of cell contents. Although pH changes per se have some effects on respiration-rates, they can be shown not to be responsible for the malonate effects described. For example, succinic acid produces its greatest stimulatory effects at pH4·0. The increased respiration brought about by this and other organic acids is inhibited by malonate at the same pH(4.0), both in carrot and beet tissue. However, results in this laboratory make it doubtful whether malonate acts in vivo only as an inhibitor of succinic dehydrogenase. Our experiments to date indicate that its inhibitory effect is not reversed by high succinic concentration or even by fumaric acid. 2. In the course of investigation of the watery extracts of different plants by the cylinder plate method on plates seeded with Staphylococcus and Bact. coli, it was found that the extracts of the seeds of radish (Raphanus sativus) gave a very marked zone of inhibition in both cases, whereas the extract of the root and the leaves did not affect the growth of the bacteria. The antibacterial principle of the extract was resistant to heat, and it could even be boiled on a water-bath for 30 minutes without a marked loss of activity. The substance responsible for the activity was isolated from the water extract of the seeds, and a syrupy liquid was obtained of boiling point 135°C under 0.06 mm mercury pressure, which could be distilled as a homogeneous substance. The almost colourless, or slightly yellow, distillate proved to be the active antibacterial principle, and has been termed 'raphanin' by us. As it was estimated on the basis of antibacterial tests, 1 kgm of the seeds contains about 6-8 gm of this active principle, the yield of the raphanin on isolation being about 3 gm per kgm of seeds. 3. It has long been known that the vitamins of cereals are not evenly distributed throughout the grain but are concentrated mainly in the outer coats and in the germ, which consists of the embryo and attached scutellum. Analyses of the meals and flours of the miller have been somewhat misleading because some mixing of the products from different parts of the grain takes place within the mills. Dr. J. J. C. Hinton, of the Cereals Research Station at St. Albans, dissected cereal grains, accurately separating the different structures, and determined the vitamin content of each structure. He reported1 that there was a surprising concentration of thiamine in the scutellum of wheat, and that although it forms on an average only 1.54 per cent of the grain, yet it contains 59 per cent of all the thiamine present in the grain. In a later paper2 he recorded that the scutellum of rye, maize and barley had similar very high contents of thiamine. This is an important matter in respect of rice milling, for it is probable that rice is not an exception and that much of the thiamine is concentrated in the scutellum. Rice is either milled raw or it is milled after parboiling. Many analyses have shown that parboiled rice is richer in thiamine than highly milled raw rice, and this agrees with the experience that beriberi is very rare or does not occur where parboiled rice is the staple article of diet. It has generally been accepted that parboiling distributes the vitamins of the pericarp and germ throughout the whole grain, and therefore milling can remove only a small amount with the bran. Recently, I have examined a large number of grains from several samples of raw milled rice and parboiled rice. The great majority of the grains of raw rice had a concavity marking the site from which the whole germ (scutellum and embryo) had been detached. On the other hand, the grains of parboiled rice did not show the concavity; but the site of the germ was flattened as though only part of the germ had been removed by milling. It appeared as though parboiling had made the scutellum more adherent, so that it had not been detached during milling. Hinton2 found that twelve hours soaking of wheat did not cause any movement of the water-soluble thiamine to the rest of the grain. He suggested that the cells of the scutellum are not permeable to water until they have been acted upon by acid chloroform or some other agent. Possibly also the high fat content of scutellum may be a bar to the penetration of water. Parboiling and also the new conversion process, which is parboiling first under vacuum and then under pressure, toughens the rice so that far fewer grains are broken during milling than in the case of raw rice; this lowering of brittleness would help the retention of the scutellum. Probably parboiling does cause some movement of the vitamins within the grain; but its chief value may be the retention of the scutellum. 4. A technique for marking mosquitoes with fluorescent compounds and watching them by ultraviolet light has been developed, to study the movements of these insects at night without affecting their normal behaviour. The method seems very promising and opens out possibilities for the study of the ecology and bionomics of mosquitoes hitherto not possible. Zukel1 used fluorescent compounds to detect marked insects in a large number of specimens, but no attempt was made to develop the technique to observe the insects at night under natural conditions. For this purpose investigations were carried out to ascertain: (a) the sensitivity of mosquitoes to shorter wave-lengths, (b) whether the insects can take up sufficient dust on their bodies to fluoresce brightly, (c) the toxicity of fluorescent compounds to insects, (d) whether it would be possible to watch the dusted insects at night by ultra-violet light, and what would be the normal range of visibility. Mosquitoes, unlike some other insects (honey bees and Drosophila), are not sensitive to the ultra-violet radiations of wave-lengths given out by the lamp used (4070-3130 A., 95.5 per cent being concentrated at 3650 A.). Both positive and negative reactions were compared to the behaviour in ordinary light. The species studied were Anopheles maculipennis var. atroparvus, Culex molestus and Aëdes œgypti. Mosquitoes take up sufficient dust to fluoresce brightly, and the dust does not shake off for a number of days. The fluorescent compounds have apparently no toxic effect on these insects as judged by their survival for more than one and a half months after.