One fact appears to dominate the whole subject of the causation of rachitis, viz., the failure to assimilate sufficient of the mineral salts required in building up the skeleton. This failure to assimilate may be caused by too meagre feeding, but even when the food is sufficiently rich, some digestive disturbance may reduce the amount absorbed below normal. This appears the only plausible explanation unless we admit Dr. Chaumier’s theory that the disease is of an infectious character. =Symptoms.= The onset is absolutely insidious and the diagnosis of rachitis is never made until nutrition has long been abnormal. This disturbance of nutrition is revealed by irregularity and abnormality in appetite, by difficulty in rising and moving about, and by the animals lying down for long periods. The subjects are feeble, sluggish and badly developed. Next supervenes the second phase characterised by deformity of bones. This is of two kinds—deformity in the neighbourhood of joints (deformity or enlargement of the epiphyses) and deformity of the diaphyses. The former results from irregularity in ossification of the articular cartilages. The latter is followed by loss of rigidity in the bones of the limbs which, under the influence of the body weight and of muscular contraction, bend in different directions. The bones appear of increased thickness principally towards the articulations. The latter are deformed, and on palpation are found to be surrounded by uneven and irregular growths. The front limbs are distorted. In young pigs, lambs, and less frequently in foals, calves and dogs, the jaws become deformed, and mastication is rendered difficult. The vertebral column may also be affected, and lordosis (bending downwards of the back) or skoliosis (lateral bending of the back) is somewhat frequent. Cyphosis, or upward bending of the back, seldom occurs, and when seen, sometimes results from disease other than rachitis. [Illustration: $1] General development is always interfered with and the young creatures are generally dwarfed. The digestive apparatus is disordered, the appetite is irregular and sometimes depraved, while indigestion, gastritis, and enteritis are not exceptional. Physiological and pathological research has shown that the quantity of phosphoric acid eliminated in twenty-four hours in a rachitic child is double the quantity passed by a healthy infant. The amount of urea in the urine (which is a criterion of nutrition, and usually varies in proportion to the amount of food ingested) is, on the contrary, diminished even when highly nitrogenous food is given, thus suggesting diminution in nutrition.