Preliminary Experiments on the Toxicity of Certain Coal-Tar Dyes for the Silkworm

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Abstract
Aqueous solutions of 21 representative coal-tar dyes were administered to silk-worms by mouth and by injection. The 11 acid dyes and 6 of the 10 basic dyes did not kill the larvae by either method of administration at a dose of 0.05 mg. per gram of body weight. The 4 lethal basic dyes were: (1) malachite green, (2) safranin bluish, (3) brilliant green, and (4) crystal violet. “By mouth” their relative toxicity was in the order just given, malachite green being the most toxic. By injection the order was (3), (1), (4), (2). Since malachite green is more toxic than acid lead arsenate for the silkworm, it might be desirable to use it for the coloring of white arsenicals and fluorine compounds to comply with such laws as may be enacted on the coloring of insecticides. Malachite green and other toxic dyes, being soluble in water and not strongly ad- sorbed by lead and calcium arsenates, might be added to the arsenicals in the form of adsorption compounds with clays, such as bentonite. When the concentration of the dye on the clay is such that it can not be washed out with water, it may still be liberated in the alimentary tract of the insect. The colorless, insoluble leuco and color bases of malachite green were not toxic to the silkworm. Neutral red, when administered by mouth, colored the integument of third-instar silkworms. The color was retained throughout the remainder of the larval stage. The suggestion is made that vital stains might be used for the identification of insects for experimental purposes. A description of the construction and operation of a simple injection pipette is given. It was used not only for the injection of dyes into silkworms, but also for the injection of organic liquids into the grasshopper, Melanoplus differentialis. Methyl alcohol, ethyl alcohol, and ether, having only a temporary effect, might be used as solvents for poisons insoluble in water. The median lethal dose of nicotine by injection into fifth-instar silkworms was about 0.0015 mg. per gram.

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