Rickets in Various Species

By the time Mellanby had described rickets in dogs, the clinical picture of the disease was well known, with enlarged epiphyses, craniotabes, rosary of the ribs, and other deviations from the normal in the skeleton. The American workers McCollum et al. (1921), Sherman and Pappen-heimer (1921), and others next induced rickets in rats, and a considerable literature on rickets in this species has resulted. A number of workers have studied rickets in dogs from various points of view, and the disease has also been induced in a number of other animals, including rabbits, guinea pigs, chicks and other domestic fowls, pigs, calves, silver foxes, and other fur animals. 

A large variety of methods have been used in the study of the disease and have contributed to our knowledge. However, the picture which can be given of the present state of our knowledge about the mode of action of vitamin D cannot be obtained by a single method of approach. The critical analysis must select its information from a great variety of studies performed in various species. The deviations from normal in the metabolism of calcium and phosphate must necessarily play a dominant role, as must the deviations from the normal in the bones themselves. Since it is a fact, however, that we know very little of the biochemical 

The present review will include for its analysis chiefly the work done in the following species man, dog, rat, and chick, as this is the basis of the greater part of our knowledge. 

The bone ash is reduced in all of them, and the disturbance in the process of ossification, as seen by the histologist, appears to be of the same nature in all. The disturbance in enchondral bone formation is the best-studied histological process. X-ray pictures show the enlargement of the growing epiphyseal cartilage in all tubular bones, although some differences occur, dependent upon the type of bone studied and also upon the species. 

In the blood, the product Ca X P is reduced in all species. The Ca may be reduced to the tetany level while a comparatively normal P value occurs, and conversely the Ca can be normal and the P greatly reduced. This result is obviously dependent on a number of variables, such as the Ca/P ratio in the diet, variations and differences in absorption of these elements, the growth rate of the body, and the deposition of salts in the matrix of the bones. 

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