MAINTENANCE 193 



protein multiplied by 1-25, digestible fat multi- 

 plied by 2' 34, digestible carbohydrates and digest- 

 ible fibre. 



This will give the amount of starch, or similar 

 carbohydrate, equivalent in nett heat value to the 

 animal to 100 Ib. of the food. 



But the experiments by which were determined 

 the nett heat values on which this calculation is 

 based were all made on animals kept on a diet 

 which was only sufficient to keep their weight con- 

 stant. Such a diet is known as a maintenance 

 ration, and starch equivalents calculated in this 

 way should be called maintenance starch equiva- 

 lents. 



The reason for using this distinctive name 

 becomes apparent when the purely experimental 

 method of finding starch equivalents is considered. 

 This method is due to Kellner who proceeded as 

 follows. An ox was kept in a respiration chamber 

 so that his total excreta, solid, liquid and gaseous, 

 could be collected, weighed and analysed. His diet 

 was then adjusted so as to maintain him at con- 

 stant weight. The diet was exactly weighed and 

 analysed. It was then increased by the addition 

 of 1000 grams of starch per day, when the weight 

 of the animal was found to increase. 



Comparison of the weight of carbon in the food 

 with the weight of carbon in the excreta showed 

 that the increase was due chiefly to storage of 

 something containing a high percentage of carbon. 



'3 



