METABOLISM 



583 



two months old and weighing 30-60 grams each and feed them daily upon a diet 

 adequate from every standpoint. 1 Such a diet may consist of casein (20 per 

 cent), butter fat (15 per cent), starch (56 per cent), salt mixture (4 per cent 2 ) 

 and yeast (5 per cent). 3 The yeast furnishes the "Water Soluble B" whereas 

 the " Fat Soluble A " is furnished by the butter fat. On the above diet the rats 

 will show normal growth (see Fig. 170) approximately doubling their weight in 



Growth in body weight Albino Rat 



FIG. 170. NORMAL GROWTH CURVES or ALBINO RATS. 

 (After Donaldson.) 



two weeks. 4 The animals should be weighed at intervals of one week. At 

 the end of two weeks eliminate the yeast from the diet leaving the diet un- 

 changed in all other respects. The diet now lacks the water soluble vitamine 

 and the animals will not only fail to grow but will show an actual loss of weight 

 A period of two weeks on this diet will be sufficient to demonstrate this fact 



*A very satisfactory form of cage in use by Osborne and Mendel may be obtained from 

 the A. B. Hendryx Co., New Haven, Conn. This cage is shown in Fig. 180. 



2 The salt mixture should have the following composition: 

 CaCO 3 134-8 gm. K 2 CO 3 141-3 gm. H 2 SO 4 9.2 gm. 



MgC0 3 . . 

 Na 2 CO 3 . . 

 KL. 



24 . 2 gm. 



34 2 gm. 



0.020 gm. 



H 3 PO 4 103.2 



HC1 53-4 gm. 



MnSO4 0.079 gm. 



gm. Citric acid -f- H 2 O . . 1 1 1 . i gm. 

 Fe citrate + 1 >iH 2 O 6.34 gm. 



NaF o . 248 gm' 



K 2 A1 2 (SO 4 )2 0.0245 gm. 



3 Fleischmann's Compressed Yeast dried in an air current at about iooC. 

 4 For other normal growth curves of albino rate see "The Rat," by Henry H. Donald- 

 son, Wistar Institute, Philadelphia, Pa. 



