_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. It may be shortly stated that the disease prevails especially on granitic or sandy soils, or on those which are mainly composed of organic debris (peat, muck). Limestone soils and those which contain any considerable proportion of potash or soda are usually exempt. _Digestive disorder_ though starting from a different point may tend to the same end. A hyperacidity of the stomach has been observed to coincide with the malady, and by interfering with easy and normal digestion, it may stand in the way of such assimilation as is necessary to vigorous health.