434 SCIENCE PROGRESS 



that these last-named requirements may not be adequately 

 satisfied but it is probably only rarely, if ever, that such a diffi- 

 culty will arise with the more complex rations of roots, fodder 

 and concentrated foods commonly given to the other classes of 

 farm stock. With a basis of roots, hay or grass and straw — 

 given fair quality — no difficulty is ever experienced in devising 

 a ration on which " thrifty" animals will maintain a good rate of 

 growth, so that apparently these materials, as a rule, effectively 

 supplement any deficiencies of constitution in other foods with 

 which they are blended. We are probably committing no 

 serious error, therefore, in assuming that the nutritive value of 

 such rations is determined essentially by their content of 

 digestible protein, fat and carbohydrate and it remains to devise 

 a satisfactory method of evaluating this content for practical 

 purposes. 



As yet only one method has been put forward which can be 

 said to rest upon a substantial basis of experimental investiga- 

 tion, viz. the method developed by Kellner, which for conveni- 

 ence may be referred to as the '.' starch equivalent " method. 1 

 This method is based upon the classical measurements by 

 Kellner of the value to the fattening adult ox of pure prepara- 

 tions of protein, oil and carbohydrate and also of a variety of 

 common feeding stuffs — in all, upwards of seventy experiments. 

 In these experiments the results of the feeding were gauged by 

 careful determinations of the gain of carbon and nitrogen by 

 the body and in every case the material under investigation was 

 compared directly with starch. In this way the relative values 

 (starch = i) to the fattening ox of the different nutrients when 

 fed separately in pure, easily digested state were found to be : 



Digestible starch = i'oo 



„ fibre (cellulose) = i "oo 



„ protein = 0*94 



„ oil = 2-41 



In applying these values to the computation of the starch- 

 equivalents of ordinary foodstuffs, it is necessary to make allow- 

 ance for factors that tend to reduce the nutritive value of the 

 foodstuff, such as the labour of mastication, etc. In other words, 

 the " availability " (Wertigkeit) for productive purposes of the 

 digested matter must be taken into account. 



1 Kellner, Die Emahrung der landwirtschaftlichen Nutztiere, iv. Aufl. 393 ; 

 Goodwin, Journal of the Board of Agriculture, xviii. 721. 





