52 REPORTS ON DIFFERENT DESCRIPTIONS OF FOOD FOR STOCK. 



REPORTS ON DIFFERENT DESCRIPTIONS OF FOOD 



FOR STOCK. 



By Robert J. Thomson, Grange, Kilmarnock. 



[Premium — Twenty Sovereigns.] 



I. Some Experiments on the comparative Feeding Values of 

 Swedes and Mangold Wurzels, 1864. 



Liebig's famous classification of food into nitrogenous and non- 

 nitrogenous, or rather, we should perhaps say, into plastic or 

 flesh-forming, and respiratory or heat-supporting, must ever be 

 regarded as having marked an important epoch in the history of 

 the chemistry of food. It opened a broad pathway through a 

 tangled forest, and afforded to all followers numerous new stand- 

 points from which to view the intricacies of animal nutrition. 

 Men of science in all parts of the world, attracted by so brilliant 

 an hypothesis, almost at once became the disciples of the 

 illustrious German. The most distinguished chemists of the age 

 immediately set about ascertaining, by laborious research, the 

 composition of almost every edible, tabulating their values in 

 the scale of nutrition by ranging them in the order of their per- 

 centages of nitrogen ; and physio] ogists, learned and unlearned, 

 set themselves, with unwonted assiduity, to examine and to 

 criticise the merits and demerits of this famous classification. 



Several years have now passed away, and the inexorable test 

 of practical experience has put it to the proof ; but, alas ! the 

 result is that the percentage of nitrogen gives, at the best, but an 

 approximate idea of the nutritive value of different kinds of 

 food, and not unfrequently altogether misleads. No one believes, 

 for example, that bran is as nutritious as flour, or that rape-cake 

 is equally valuable with linseed-cake, yet their percentages of 

 nitrogen are practically identical. We believe, notwithstanding 

 the able critiques of certain physiologists, that Liebig's hypo- 

 thesis, looked at in the most liberal light, is, in the abstract, 

 theoretically correct, but that it fails in ordinary practice, simply 

 because circumstances and conditions modify or invalidate the 

 deductions from chemical analyses as ordinarily made. We all 

 know that the corrosive action of a strong acid is entirely neutra- 

 lised when in combination with an alkali, which combination 

 possesses properties entirely different, not only from the acid 

 itself, but also from all other combinations of the same acid with 

 other alkalies. And so it is with nitrogen in the much more 

 complicated and exceedingly intricate organic compounds which 

 form the food of animals — compounds, many of which chemistry 

 has not yet even pointed out with distinctness, and regarding the 

 properties of which nothing is positively known. It is a remark- 



