Some aspects of the toxicology of hydrocyanic acid in ruminants

Abstract

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 best results. 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 plant. 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.