In the final stages, the bones may be cut with a knife, and a time arrives when bony tissue seems completely to have disappeared; thus, as shown in Fig. 8 herewith, it was possible to cut the entire head of a pig into thin slices without the slightest difficulty. All parts of the head had been affected by the softening change. From the chemical point of view, the diminution in mineral salts and in phosphate of calcium has long been recognised, but the degree of this change varies according to the phase. In human beings the proportions have been estimated as follows: Normal bone, 50 to 80 per cent. of phosphate of calcium; bone in persons suffering from osteomalacia, 5 to 20 per cent. of phosphate of calcium. The changes in the ossein have not been carefully studied. We only know that histologically the ossein becomes fibrillar, and that chemically it no longer retains its normal composition. =The diagnosis= is difficult, particularly on the first occasion of seeing the disease, and especially if this is of an enzootic character. The practitioner may also have some hesitation in diagnosing isolated cases in regions where the disease seldom occurs. Otherwise, diagnosis is usually easy, as soon as lameness or synovitis, or arthritis of the lower regions of the limbs appears. Only in isolated cases are the lesions likely to be mistaken for accidental injuries, and it is also fairly easy to differentiate them from the localised lesions of rheumatism. The latter disease seems more frequently to attack the upper joints of the limbs, and is often accompanied by intense fever and cardiac disturbance. =Prognosis.= In a general sense the disease is very grave, because it appears as an enzootic, and, in dry years and those during which there is a scarcity of forage, inflicts enormous losses on the breeders of certain countries. When advice is sought towards the end of the second phase of the disease the prognosis is therefore very grave. Under such circumstances it is often better to slaughter rather than to treat, provided that the affected animals, like cows, pigs, or goats are still of some value. =The prognosis= is much more hopeful if treatment is attempted at an early stage, when improved diet and the use of suitable drugs sometimes lead to recovery. =Treatment.= We know that in the Middle Ages this disease was often treated by the administration of crushed bones, and even at the present day ground bones are frequently recommended. Treatment must be subordinated to proper feeding, no system of medication being of any value whatever unless the food is suitable.