566 poisons : their effects and detection. [§§ 745, 746. 
pound of arsenic. It therefore follows that the coloured substance 
should not contain more than 70 per cent, of arsenious acid. The Act 
applies to all the colourless preparations of arsenic ; but it is not to 
affect chemists in making up prescriptions for medical men, or in 
supplying medical men ; nor is it to affect the wholesale dealers in 
supplying arsenic to retail shops, etc. The penalty for conviction is 
£20, or less. 1 
§ 745. Dose. —The smallest single dose of solid arsenic said to have 
proved fatal to a human being is -16 grm. (2J grains). Farriers and 
grooms are in the habit of giving as much as 1*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. (J grain), and even 
this may, in the smaller kinds, cause illness. 
Witthaus 2 states: “A careful search through the medical and 
pharmaceutical periodical literature has failed to bring to light any record 
of the clearly established death of an adult from a single dose of less 
than 2 grms. (30 grains) of arsenic in the solid form.” It is therefore 
a matter of interesting speculation as to what fact or facts the majority 
of toxicologists have relied upon in stating as a possible fatal dose 
•1 to -2 grm. (1J to 3 grains). 
Letheby’s case ( Lancet , 1847), of a young woman who died after taking 
fly-water containing 2|- grains of white arsenic, is not satisfactory, for 
the post-mortem appearances rather pointed to death from cerebral 
hemorrhage. 
There is a case reported by H. T. Castle in which a woman, after 
recent abortion, took 2 grains of arsenic in solution and died. Probably 
she would have recovered from the abortion had she not taken the 
arsenic, but the pathological appearances showed a good deal of septic 
mischief, so that it is not a case supporting the minimum lethal dose of 
2 grains of solid arsenic. 
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. (J to 1 grain) for a dog. 
§ 746. 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 
1 Commercial arsenic is often much adulterated, especially with gypsum, chalk, 
etc. These are most readily detected by subliming the arsenic. The sublimed 
arsenic itself may not be entirely pure, sometimes containing arsenical sulphide 
and antimonious oxide. 
2 Manual of Toxicology, 2nd ed., Lond., 1911. 
