It will be seen from the foregoing, that three dietary factors at least are concerned primarily in the development and normal metabolism of the skeletal tissues. These are the phosphorus and calcium content, and the content of the organic substance which we may provisionally designate as the anti-rachitic substance, although this is not an entirely satisfactory term since this substance is not a preventive of rickets in the sense that the anti-beri-beri substance or the anti-scorbutic substance are respectively preventives of beri-beri and scurvy. The organic substance under discussion may exert an anti-rachitic effect, but so also may phosphorus or calcium, depending on the peculiar constitution of the diet.

Rickets, it will be seen, is not a deficiency disease in the same sense as are beri-beri, scurvy or the ophthalmia of dietary origin. Beri-beri, scurvy and ophthalmia, so far as we can now see, are due to specific starvation for one (possibly more) organic substance, peculiar to each disease, whereas rickets has at least three etiological factors, disturbances of the ratios among which will effect the structure of the bones.

It is now easy to appreciate, in the light of the experiments just described, that rickets must be studied in a special way if satisfactory results are to be secured. Isolated observations cannot well be correlated and interpreted. It is essential that the effects on the structure of the osseous system, of deviation from the optimal relations with respect to all factors which can be shown to enter into the etiology of rickets and related disturbances of bone growth, be systematically studied in a very comprehensive way before a complete explanation can be given of this most interesting problem in pathology.