150 



Scientific Proceedings (120). 



the anemias of the von Jaksch type). The rachitic involvement 

 of the head in the children suffering from the combined conditions 

 appears to be out of all proportion to the involvement of the 

 extremities. Rickets is associated with the most severe forms of 

 chronic interstitial nephritis or developmental defects of the kid- 

 ney in which there is the most extreme degree of disturbance in 

 renal function. Curiously, tetany sometimes occurs with rickets 

 and sometimes not. Since the conception that there might be 

 more than one kind of rickets was supported solely by clinical ob- 

 servations of at most a suggestive character, we did not feel at 

 liberty to express it as a definite hypothesis. Recently, however, 

 our experiments have yielded results which indicate that there 

 may be two distinct forms of the disease. 



II. The experimental evidence. 



In previous publications 1 we have described certain defective 

 diets which, when fed to the young rat, produced marked dis- 

 turbances in the growth and calcification of the skeleton. The 

 diets in question were all insufficiently supplied with a factor or 

 factors present in cod liver oil. They differed from each other 

 considerably, however, in the composition of their mineral fraction, 

 chiefly, however, as regards the calcium and phosphorus. They 

 may be divided into two groups according to the relative amounts 

 of those two elements present. In one group, the phosphorus was 

 at a low level but the calcium at or above the optimal level; in 

 the other group, on the other hand, the calcium was at an extremely 

 low level but the phosphorus was not far from the optimal. 



When the diets of the first group (the phosphorus being 

 deficient and the calcium-phosphate ratio high) were fed to young 

 rats living under ordinary laboratory conditions (room light), 

 there developed a diseased condition of the skeleton which was 

 identical in all essential particulars with that seen in the rickets 



1 McCollum, E. V., Simmonds, Nina, Parsons, H. T., Shipley, P. G., and Park, 

 E. A. Jour. Biol. Client., 1921, xlv, 333. 



Shipley, P. G., Park, E. A., McCollum, E. V., and Simmonds, Nina. The 

 Johns Hopkins Bulletin, 1021, xxxii, 160. 



McCollum, E. V., Simmonds, Nina, Shipley, P. G., and Park, E. A. Amer. 

 Jour, of Hygiene, 1921, i, 492. 



McCollum, E. V., Simmonds, Nina, Shipley, P. G., and Park, E. A. Jour. 

 Biol. Chem., 192 1, xlvii, 507. 



