.Rickets does not occur among wild animals, but is common among wild creatures kept in confinement. This is especially true of monkeys and young carnivora kept in zoological gardens. Dogs, especially the larger breeds, are very prone to develop rickets, whereas cats are said to remain free from the disease under domestication. This fact is of great significance, since the cat rarely fails, even when domesticated, to kill birds and small rodents in considerable numbers, and to remain in a measure on the type of diet characteristic of wild carnivora, whereas dogs are less enterprising as foragers, and rely upon the food provided by their masters. Herbivorous animals such as the horse, cow, sheep, pigs and others do not frequently exhibit skeletal defects where a pasturage is available. It will be shown later that these facts can be satisfactorily explained on the theory that the diet is the most important factor in the etiology of rickets.