Fig. 477. - Actinomyces Bovis.
1, The fungus on cow's tongue; 2, Cell or group of cells with actinomyces; 3, Clubbed filaments and centre filaments of the fungus; 4, Filaments from the centre enlarged.
It is a curious circumstance that some of these poisonous plants may be eaten for a considerable time with perfect impunity. The yew, for-example, only manifests its poisonous quality on certain occasions, and the same thing is true of potatoes, the poison of which seems to lie chiefly in the skin, and horses which have consumed large quantities of them uncooked have died rapidly with symptoms of poisoning. Potatoes, or potato skins, however, appear to be perfectly harmless when boiled. Some foods become injurious in consequence of defective modes of preparation; for example, hay which has been highly dried or burnt in the making. Foxy oats, so called on account of the red colour which they assume as the result of having been exposed to moisture and subsequently dried in kilns, assume a decidedly poisonous character, acting chiefly on the kidneys. Numerous cases of the poisoning of cattle have been traced to the consumption of large quantities of frozen turnips.
Of the rapidly poisonous action of the yew under certain circumstances there is no doubt. Many instances have occurred where yew clippings have been thrown over a fence, and a considerable number of animals which had partaken of it have been found dead, or seen to be in a dying state, with the symptoms of narcotic poisoning. Yet horses have been known to graze for years in pastures the hedges of which were mainly composed of yew, and nothing has happened; when suddenly the introduction of one or two strange animals has been followed by the death of them from eating a small quantity of yew.
Perhaps in the majority of cases the animals which remain unaffected in the pastures do not eat the yew at all, and it is certainly the case that in experiments which have been made, some of them lately, the greatest difficulty has been met with in persuading the horses to eat the yew which was supplied to them, and it was always necessary to keep them without other food for a considerable time. In some experiments which were performed a few years ago a sheep, after being kept without food for two or three days, ate, in the course of twenty-four hours, 14 oz. of the dried leaves of the yew, and two days later it ate 6 oz., yet no effect was observed. A yearling heifer ate in twenty-four hours 2 lb. 6 oz. of half-dried leaves and twigs without effect. Three calves, about seven months old, consumed in two hours 3 lb. 6 oz. of half-dried leaves and twigs without effect. Three days later the same calves ate 10 oz. in two hours, and two days afterwards one of the calves was noticed to be ill, and in half an hour it died. A donkey ate in twenty-four hours 5½ oz. of half-dried leaves without effect, and two guinea-pigs consumed l½ oz. of dried leaves in seventy - two hours without suffering any inconvenience. In another instance experiments were tried with the yew leaves, some of which had been eaten by a valuable filly on the first night of entering the pasture, and which was found dead on the following morning. Some of the leaves from the plant of which the filly partook were given to three guinea - pigs, mixed with bran and oats. Ten days afterwards, the feeding being continued during the whole time, one of the guinea-pigs died. On the following day a second one died, and four days after, the third guinea-pig died. On post-mortem examination it was found that the stomach in each case was perfectly empty, the lining membrane of the intestines much congested, and the tube was filled with well-digested leaves of yew. Two sheep and a horse were hurdled on the same pasture and supplied with the yew leaves, but they steadily refused to touch them. The horse was subsequently placed in his stable and a quantity of yew leaves, finely chopped, were mixed with the ordinary food and placed in the animal's manger, where it remained for the whole of the day without being eaten. On the follow-ing morning, however, the animal was found dead, and its manger was empty. It would appear in this case that the particular plant, the eating of which led to the death of the valuable filly, did possess actively poisonous qualities, at least for horses and guinea-pigs. The sheep which were made the subject of the experiment escaped by refusing to eat the plant.
Acorns are well known to be a useful article of diet under ordinary circumstances, and in places where they are abundant. On common lands they are carefully collected and sold by the collectors as food for horses, cattle, and sheep. Pigs thrive upon them, and the passage rights in forests where oak - trees are abundant are valued on account of the opportunities which the owners of pigs have to turn them into the forest when the acorns are falling. Sheep and cattle also take acorns freely, usually, if not invariably, when mixed with other food; but several serious outbreaks of acorn poisoning from time to time have occurred, attended with fatal results, when, owing to a long drought, the herbage has been extremely scanty, and the animals have, therefore, been induced to live on the acorns almost exclusively. The disease from which the cattle have suffered is not in any way due to the indigestible character of the food. Occasionally, in seasons when acorns are very abundant, cattle and sheep, and even pigs, have suffered from a too free indulgence of a favourite food, and some of the animals have died from the impactment of quantities of the nuts in different parts of the digestive system; but this is not what is intended by the term acorn poisoning. On the contrary, in the true disease the most marked symptoms are not present until a considerable time after the acorns have been digested, and no trace of them is to be found on post-mortem examination. Of course this fact might be interpreted to mean that the animals have not died from the consumption of acorns, but the evidence is too clear to admit of any question.
In 1868, when the malady was first recognized, a large herd of cattle, which were feeding in a park where acorns were very abundant and pasture very scanty, became affected, while other cattle on the same estate, separated from the diseased ones only by an iron fence, which shut them off from the acorns, remained perfectly well. The symptoms were not at all violent in their character. In the first instance, after a week or ten days' feeding on the acorns, instead of improving in condition, the animals began to waste, and presented a remarkably listless and dull appearance. The appetite in the worst cases was entirely lost, and it was remarked that when the disease got to that stage the animal never recovered, but lingered on for some time, and was ultimately found dead on the pasture.
Careful analyses were made, but no special organic poison was discovered - nothing, in short, which could be suggested as a possible cause of injury except tannic and gallic acids. It may be observed in this connection that the detection of an organic poison is extremely difficult; in fact, the failure of discovery is by no means evidence that it does not exist. Since 1868 several similar outbreaks have occurred, usually under the same conditions, i.e. a hot, dry summer, deficiency of grass, and the prevalence of high winds in the autumn, causing the fall of a quantity of acorns before they are perfectly ripe. On the other hand, these climatic influences have prevailed in many years when no outbreak of acorn-poisoning has occurred.