Rickets was formerly much more common among the poorer classes than among the well-to-do. It occurs much more frequently in the winter and spring than at the other seasons, and is much more prevalent among bottle-fed infants than among nursed infants. It occurs not infrequently in infants who are breast-fed. It is not uncommon to see severe rickets develop in negro children who are fed almost entirely at the breast. The following table from data collected by Miss Ferguson (2) shows the relation of rickets in the children of Glasgow to length of time at the breast in months.

Since breast-feeding has been generally regarded in the past as assurance that the diet of the infant will be of satisfactory quality, data such as are recorded in the table on page 300 would be interpreted by most people as a strong support for the view that the character of the diet has little or nothing to do with the etiology of rickets. In recent years, however, there has been brought to light more and more evidence of an experimental nature, which casts doubt upon the adequacy of breast milk as a food, where the diet of the mother is not wisely chosen.

The studies of Ferguson further emphasize the importance of the time of year in influencing the development of rickets. Of 349 children observed by her, 232 ceased to thrive between December and May, against 117 who developed rickets during the other half of the year. Thompson (6) has also recently emphasized the effect of the winter season in inducing this disorder.