§ 719. Dose.—The smallest dose of arsenic known to have proved fatal to a human being is ·16 grm. (21⁄2 grains). Farriers and grooms are in the habit of giving as much as l·3 grm. (20 grains) a day to a horse, so that the poisonous dose for this animal must be very large.
The maximum dose for the horned cattle appears to be from ·32 to ·38 grm. (5 to 6 grains); that for a dog is 16 mgrms. (1⁄4 grain), and even this may, in the smaller kinds, cause illness.
The following may be considered as dangerous doses of arsenic:—·13 grm. (2 grains) for an adult; 1·9 grm. (30 grains) for a horse; ·64 grm. (10 grains) for a cow; and 32 to 64 mgrms. (1⁄2 to 1 grain) for a dog.
§ 720. Effects of Arsenious Acid on Plants.—If the root or stem of a plant is immersed in a solution of arsenious acid, the hue of the leaves soon alters in appearance, the green colour becomes of a whitish or brownish hue, and the plant withers; the effect being very similar to that produced by hot water. The toxic action may be traced from below upwards, and analysis will detect minute quantities of arsenic in all portions of the plant.
It has, however, been shown by Gorup-Besanez,[716] that if arsenious acid be mixed with earth, and plants grown in such earth, they only take up infinitesimal quantities of arsenic. Hence, in cases of cattle poisoning, any defence based upon the alleged presence of arsenic in the pasture will be more ingenious than just.
[716] Annal. d. Chemie u. Pharmacie, Bd. cxxvii., H. 2, 243.
The influence of arsenical fumes as evolved from manufactories upon shrubs and trees is in general insignificant. Pines and firs, five to six years old, have been known to suffer from a disease in which there is a shedding of the leaves, the more tender herbage being at the same time affected. Whatever dangers the practice of steeping corn intended for seed in a solution of arsenious acid, as a preventive of “smut,” may possess, it does not appear to influence deleteriously the growth of the future plant.
Superphosphate of manure is frequently rich in arsenic. Dr. Edmund Davy asserts that plants to which such manure is applied take up arsenic in their tissues, and M. Andonard has made a similar statement. Tuson[717] has also undertaken some experiments, which confirm Andonard and Davy’s researches. The bearing of this with relation to the detection of arsenic in the stomachs of the herbivora needs no comment.