XI.] STARCH EQUIVALENTS 215 



constituents possess in each food when deduction has 

 been made for the work spent in digestion. In order to 

 arrive at a convenient number for our comparisons, we 

 shall take starch as a basis and reduce the digestible 

 constituents of the other foods into terms of their 

 equivalents of starch. For example, we have just seen 

 that a pound of digested fat in the food will give rise to 

 half a pound of fat in the increase, whereas a pound of 

 starch only gives rise to a quarter pound of fat in the 

 increase ; so that if we call 100 the value of starch, then 

 we should have to express the value of fat by 200. 

 Similarly, pure protein has a fat-making value about 90 

 per cent, of that of starch, so that the equivalent in 

 starch of 100 of protein would be 90. In this case we 

 are dealing with pure food constituents, but exactly the 

 same principle may be followed for each feeding stuff as 

 a whole. We can obtain a single number which repre- 

 sents the number of pounds of starch which would have 

 the same fattening effect as 100 lb. of the food 

 in question. This starch equivalent represents the 

 summing up of the value of the fat, protein, carbo- 

 hydrates, and fibre respectively in the food, after the 

 deduction brought about by the work spent in digestion. 

 Table XVII., with its list of food compositions and 

 digestible constituents, also gives the starch equivalents, 

 which range from as high as 120 for linseed to as low as 

 1 1 for wheat straw. Such a table of starch equivalents 

 forms the only sound basis for the comparison of the 

 value of feeding stuffs, and though there are many other 

 factors to be taken into account in making up rations 

 for farm animals, these figures should be considered in 

 deciding which are the cheaper of the concentrated 

 feeding stuffs which can be purchased, and also in what 

 quantities they should be used to replace one another 

 in a ration. Of course they refer only to the fattening 



