=Causation.= The problem of why osseous cachexia occurs has naturally given rise to numerous explanations, some plainly inadmissible, others, however, of greater or less plausibility. The fact which, from the earliest times, appears to have attracted most attention is the relation defective nourishment bears to development of the disease. In Norway, as early as the year 1650, the plant known as sterregraes (which renders animals dull and heavy) was thought to be the cause of the disease; two centuries later, in 1846, the _Anthericum ossifragum_ was similarly regarded. Zundel, in 1870, claimed that the Germans first referred the development of the disease to chemically incomplete forms of nourishment. This opinion seems fully confirmed by the remarkable observations of Germain on European horses imported into Cochin-China, and it is finally placed beyond question by the work of Cantiget. Basing his researches on analysis of the soil, he proved that osseous cachexia only occurs in cattle depastured on land which is too poor in phosphoric acid and calcium phosphate, and that it can be banished by enriching the soil with suitable manures up to a point when the proportion of phosphoric acid becomes normal. In good land, suitable for raising cattle, the proportion of phosphoric acid, according to the best exponents of agricultural chemistry, should not fall below 4,000 kilograms to the hectare. Cantiget and Brissonet have shown that where the soil contains less than 1,500 kilograms to the hectare, osseous cachexia is almost permanently present. As soon, however, as this proportion is raised above 2,000 kilograms by suitable culture, the losses diminish, and the cachexia finally disappears. This view was greatly strengthened by fodder analyses, which showed that in all cases where the soil is poor in calcium phosphate, the forage is poor in phosphoric acid, and _vice versâ_. The food is too poor in mineral salts, firstly for normal development; and secondly for the proper nutrition of the skeleton. Germain is of a similar opinion with regard to the occurrence of osseous cachexia in horses in Cochin-China, where the soil is very poor in lime. The fodder and cereals are poor in mineral salts, and even when given in large quantities do not furnish proper (chemical) nutrition. Clear proof of the correctness of this view is afforded by the fact that feeding with forage and cereals obtained from France or Algeria prevents the disease appearing, or diminishes and finally removes the previously existing symptoms. Furthermore, Germain shows that Europeans, living solely on the products of the country, to some extent suffer like the horses. This theory though based on sufficiently solid foundations to carry conviction, has been questioned, and it may be desirable to record briefly the criticisms advanced against it. One of the most important is as follows:—