Of the various methods the ferric thiocyanate method is selected for the
determination of hydrocyanic acid both in plants and in animal organs. It
is shown that erroneous results may be obtained in certain plants by the
alkaline titration method. The ferric thiocyanate method is dealt with in
detail and several modifications introduced. It is demonstrated that the
method yields excellent results. For the liberation of hydrocyanic acid from
the material to be analysed the aeration procedure is adopted as it yields the
The sources of hydrocyanic acid in cases of poisoning- in stock are
discussed and the results of the examination of a large number of plants for
hydrocyanic acid are given.
The factors concerned in the causation of poisoning of animals by cyanogenetic
plants are discussed in detail and these factors include the quantity
of the plant ingested; the previous diet of the animal; the hydrogen-ion
concentration of the stomach contents; the percentage of the total hydrocyanic
acid in, the plant which it; present in the free state; the quantity of
enzyme present in the plant; and the hydrocyanic acid content of the plant.
In connection with the last-named factor, a detailed discussion is given on
the manner in which it is influenced by the following: soil; climatic conditions;
age of the plant; variety of the specimen; individual variation; part
of the plant; and the state of the plant. The variability of the hydrocyanic
acid content of cyanogenetic plants is illustrated by graphical representations
of the hydrocyanic acid content, over a number of days, of Dimorphotheca
Ecklonis and four strains of Cynodon plectostachyum. The effect of wilting
on the hydrocyanic acid content is clearly shown. It is pointed out that the
danger, which a cyanogenetic plant constitutes to stock, should be judged on
the maximum quantity of hydrocyanic acid which can be developed by the
The physiological significance of cyanogenesis in plants is discussed.
The ruminal contents and livers of sheep which had died at this Institute
from causes other than poisoning by hydrocyanic acid were found to contain
only traces of hydrocyanic acid. Hydrocyanic acid was, however, frequently
demonstrable in relatively large quantities in the ruminal contents of
animals, which had died from causes, other than hydrocyanic acid poisoning,
under field conditions. Of the organs of sheep which were poisoned by hydrocyanic
acid per os, the ruminal contents and liver contain the largest quantities
of hydrocyanic acid of the organs analysed. The quantity of hydrocyanic
acid ingested is shown to be reflected in the hydrocyanic acid content of the
ruminal contents and liver. The hydrocyanic acid content of the liver and
ruminal contents of approximately twenty sheep which had received varying
quantities of hydrocyanic acid was determined. In the case of the liver the
hydrocyanic acid content was 0·14 mg., or more, per 100 gm. in sheep which
had received lethal quantities, or less than 0·14 mg. per 100 gm. in sheep
which had received sublethal quantities of hydrocyanic acid per os. The
corresponding value for the ruminal contents is approximately 1·0 mg. of
hydrocyanic acid per 100 gm. The relative value of the hydrocyanic acid
contents of the liver and ruminal contents in arriving at a diagnosis of
hydrocyanic acid poisoning is discussed. It is shown: that the. hydrocyanic
acid content of the ruminal contents serves as corroborative evidence for the
hydrocyanic acid content of the liver and that it is essential to know the
latter in order to arrive at a definite diagnosis. During decomposition of
organs of animals, not poisoned oy hydrocyanic acid, significant quantities
of hydrocyanic acid did not develop. It is demonstrated that hydrocyanic
acid rapidly disappears from the liver but more gradually from the ruminal
contents when they are allowed to decompose. Mercuric chloride was found
to be an excellent preservative of ruminal contents and liver and completely
prevented the disappearance of hydrocyanic acid from these materials during
storage. This fact renders it possible to submit specimens of liver and
ruminal contents to a laboratory for analysis.
It was demonstrated that
in the intact animal, considerable diffusion of hydrocyanic acid occurs from
the stomach contents into the liver after death.
The problem of chronic hydrocyanic acid poisoning is fully discussed.
The experimental work of the author did not result in the production of
chronic hydrocyanic acid poisoning in sheep. From the literature on the
subject, available to the author, it is evident
(1) that some authors .have produced chronic hydrocyanic acid poisoning in the form of injury to the central nervous system in rabbits
and monkeys, and, '
(2) that other authors have demonstrated the goitrogenic activity of
hydrocyanic acid in various combinations.
It is shown, however, that the experimental conditions for the production
of these forms of poisoning are such that it is very unlikely that they
will occur naturally in stock.