234 THE CHEMISTRY OF CATTLE FEEDING 

 Method. Try equal quantities of the two foods. 



Protein. "Starch." N-ratio. 



Lbs. Lbs. 



ioo Ibs. Cake contain ... 25 56 



loo Rice ,, ... 6 65 



200 ,, Mixture ,, ... 31 121 4 to i 



The quantity of protein is about three times, and the 

 starch is twice, as much as is required. It is necessary, there- 

 fore, to take smaller quantities of both foods and a smaller 

 proportion of cake. Try half the quantity of rice and a fourth 

 of the cake. 



Protein. "Starch." N-ratio. 



Lbs. Lbs. 



25 Ibs. Cake contain . . . 6*25 14*0 



50 ,, Rice ... 3-00 32-5 



75 Mixture ,, ... 9-25 46-5 5 to I 



This contains too little protein and much too little " starch," 

 so more rice must be used. 



Protein. "Starch." N-ratio. 



Lbs. Lbs. 



25 Ibs. Cake contain . . . 6*25 14-00 



75 Rice ... 4-50 4875 



100 Mixture ,, ... 1075 6275 5-9 to I 



The proportions are now nearly right, but the quantities 

 are too large. By further guessing and testing the result, it 

 can be shown that 22\ Ibs. of cake and 73 Ibs. of rice meal 

 together contain very nearly the required quantities of protein 

 and starch. This method is, however, clumsy, tiresome, 

 unscientific, and unsatisfactory in all respects. The exact 

 result can be found much more quickly and more easily in 

 other ways. 



Arithmetical Method. Consider, first, the simple case 

 of a dietary having an N-ratio of 6 to i, and two foods (a) and 

 (b) having N-ratios of 5 to i and 7 to i respectively. It is 

 evident that the excess in (a) is exactly equal to the deficiency 

 in (b). If the N-ratio in (a) were 4 to i, the excess would 

 be twice as great as the deficiency in (b), and it would be 

 necessary to take two parts of (b) to one of (a). The required 



