318 THE VITAMINS 



with the line test and regard the latter as somewhat more sensitive. 

 However, they recommend the use of radiographic observations to 

 determine when to begin the test period and to follow the progress of 

 the test. 



X-ray and Histological Studies of Bone. — Early in 1921 Sherman 

 and Pappenheimer (1921, 1921a) had pointed out that, in their experi- 

 ence, the following diet regularly produced marked rickets in rats : 



Diet No. 84 



Per Cent 



Patent flour 95.0 



Calcium lactate 2.9 



Sodium chloride 2.0 



Ferric citrate 0.1 



while the introduction of 0.4 per cent secondary potassium phosphate in 

 place of an equal weight, i.e., replacing about one-seventh, of the calcium 

 lactate contained in the rickets-producing diet, completely prevented the 

 development of the rachitic lesions, although it was without influence 

 upon the growth and body weight. Diagnoses of rickets were based upon 

 X-ray studies during life and gross changes found in the thorax and 

 long bones at autopsy, as well as upon microscopic examination of 

 sections of ribs. 



The Diet No. 84 of Sherman and Pappenheimer (1921, 1921a) was 

 originally published without further elaboration because it afforded a 

 then-much-needed key to the dietary production of low-phosphorus 

 rickets. The ease, promptness, and regularity with which it permits the 

 experimental induction of the characteristic bone condition has led some 

 investigators to use it as a basal rickets-producing diet in studies of 

 vitamin D values ; but it was obviously never offered as in any sense a 

 parallel to the basal diets used, for example, in studies of vitamin A, B 

 and C values of food — diets adequate in all respects except for the 

 vitamin in question. Pappenheimer et al. (1921) suggested modifications 

 in this direction, and Sherman and StiebeHng (1929, 1930), as described 

 further on in this chapter, approximated the ideal of a basal diet excel- 

 lent in all other respects but lacking vitamin D — a diet which made 

 vitamin D the sole limiting factor and therefore permitted of its uncom- 

 plicated measurement; but which was not in the strictly literal sense a 

 rickets -producing diet. As described later, this and a number of related 

 objectives are embraced in a very far-reaching plan of experimental 

 dietary modification now being developed by Mendel and his coworkers. 



When "Diet 84" is used as a basal diet in tests for vitamin D, its 

 drastically rickets-producing deficiencies may result in materials being 



