The occurrence of arsenic as an occasional constituent of plants has been recognised for many years. Chatin (1845) found that if a plant were supplied with arsenical compounds at the roots arsenic was absorbed, but that it was distributed unequally to the various tissues. The greatest accumulation of the element was in the floral receptacle and the leaves, while it was scarce in the fruits, seeds, stems, roots and petals. E. Davy (1859) commented on the presence of arsenic in plants cultivated for food. He grew peas in pots and watered them for a short time with a saturated aqueous solution of arsenious acid, the application being then discontinued. The plants, apparently uninjured by the treatment, flowered and formed seeds. On analysis arsenic was readily detected in all parts of the plant, including the seeds. Other analyses revealed the presence of the element in cabbage plants (from pots) and turnips (from field), both of which had been manured with superphosphate containing some amount of arsenic. This absorption of arsenic by the roots of plants was further established by Phillips (1882). Various physiological workers have pointed out that this element is frequently or usually present in animal tissues. Cerný (1901) reached the general conclusion that minimal traces of arsenic can occur in animal organisms, but that these play no part in the organism and indeed are not constant in their occurrence. Bertrand (1902) established its presence in minute quantities in the thyroid glands of the ox and pig, hair and nails of the dog, and the feathers of the goose. Gautier and Clausmann (1904) realised the constant presence of arsenic in human tissues and recognised that it must inevitably be introduced into the body with the food. This led them to estimate the arsenic present in various animal and vegetable foods, some of their results being given in the following table. _Arsenic per 100 parts fresh substance in µ gr._ (= thousandth part of a milligram)[8]. Wheat (Victoria--complete grain) ·7 „ (from Franche Comté) ·85 White bread ·71 Whole green cabbage ·2 Outside leaves of cabbage ·0 (absent) Green haricots ·0 „ Turnip ·36 Potatoes 1·12 [8] 0^{µ gr.}, 1 = 0·0001 mg. Arsenic was also found in wine and beer and in considerable quantities in sea water and various kinds of salt. Since it cannot be found in some things even in the least traces, the authors conclude that it is incorrect to say that the element is always present or that it is essential to all living cells.