Symptoms. Ruminants without any appreciable cause, lick the clothes of their care-takers, chew and swallow articles of clothing of all kinds, bones, old shoes, gloves, socks, cuffs, collars, small forks, pocket-knives, nails, wires, needles, coins, stones, lumps of clay, hair, which may give rise to secondary troubles of a more or less serious kind. Pregnant cows are especially subject to this infirmity. The small pointed objects like pins, needles, ends of wires, etc., which are mostly taken by accident with the food are especially apt to be entangled in the alveoli of the reticulum and make their way to the heart, with fatal effect, or through the abdominal walls creating a fistula. Hair aggregates with saliva, mucus and phosphates, to form balls in the first two or three stomachs. Other indigestible objects may also become encrusted and prove sources of irritation. Licking the skin of another animal is doubtless at times encouraged by the taste of the salts of perspiration, but in other cases it has all the appearance of a mutual kind service as the cow with itching head will walk up and present it to its fellow which rarely fails to respond to the invitation. Stump licking is not uncommon.
Sheep shut up in the winter get in the habit of chewing each other’s wool, thus virtually depilating their fellows and accumulating wool balls in their stomachs.
Pigs when running at large eat human fæces often infecting themselves with the cysticercus cellulosa, and devour their own or their fellows’ bristles, which form ovoid and irritating aggregations in the stomach.
Puppies are proverbial for swallowing every small object that comes in their way, coal, pebbles, marbles, leather, hair, etc., with the result of inducing nausea and vomiting, or more seriously, wounds of the stomach, gastritis and enteritis. In older dogs the habit is more likely to imply rabies.
Solipeds will lick and swallow each others hair, eat off the hair from each other’s tails and manes, eat their clothing, lick the wall plaster, earth or sand, and even the manger or rack. The last named habits are usually connected with disease.
Fowls can digest almost anything they swallow, but if they take to picking their feathers, they create serious injury to the skin and indirectly to the general health.
Causes and Nature. In general terms it may be said that the causes of depraved appetite are very numerous, so that the trouble must be looked upon as a symptom of many morbid conditions in place of a disease sui generis.
Heredity has been invoked as a cause, mainly, it would appear, because the disease appears enzootically on certain exhausted soils, or in herds kept in the same unhygienic conditions. In such cases the real cause is usually to be found in faulty conditions of soil, water, buildings, food, etc., on the correction of which the trouble disappears. When, however, from a long continuance of unhygienic conditions, a weakness of constitution is transmitted from parent to offspring, such hereditary debility may be accepted as a predisposing factor.
An exhausted soil, lacking especially the elements of lime and phosphorus, is a common cause, though by no means the only one. Nessler who analyzed the hay and water, furnished to cattle suffering from this disease in the Black Forest found a notable absence of the soda salts. In others in which osteo malacia was the prominent symptom the lack was in phosphate of lime as well. In the nature of things the soil that has been continuously cropped to exhaustion is robbed of both earthy and alkaline salts, and the animals fed on its exclusive products suffer not only as regards the nutrition of the bone, but also of the soft parts. Hence Trasbot says that in osteo malacia, pica is never absent. Roloff and Röll hold that it is the first symptom of osteomalacia. In South Africa where the land has been cropped with oats year after year without manure and as long as it will bear, the disease became prevalent in the street car horses fed on the oats, and was corrected by the addition of phosphates, or phosphate bearing food, to the ration. In the older dairying farms of New York which have been kept under grass for a great length of time, and all the milk products sold off, depraved appetite in all its forms is quite frequent. Where the land is originally light and sandy and naturally deficient in lime, osteo malacia is often a concurrent disorder. The two conditions may however occur independently of each other, and especially may pica appear alone, in keeping with the greater solubility of the soda and potash salts and the readiness with which these can be washed out of the soil, while the less soluble lime salts in part remain.
Lemcke, Haubner and Siedamgrotzky attribute the disease to a nervous disorder. Lemcke indeed traces the disorder to a lack of phosphorus, and claims that osteomalacia only supervenes where the rheumatic diathesis is also present.