EARLY THEORIES OF NUTRITION 241 



values" may be instanced ; in 1809 he published a table of all 

 the recognised cattle foods, ranged in order and marked to show 

 how much of each was equivalent to 100 parts of hay taken as 

 a standard. Thaer's hay values were based partly on his own 

 experience as a practical man and partly on attempts, very 

 imperfect in the then state of chemical knowledge, to estimate 

 by analysis the nutritive constituents of the foods. Boussingault's 

 investigations were the earliest serious attempts to apply scien- 

 tific principles to the feeding of animals ; the importance of the 

 nitrogenous constituents of food had now become clear, so his 

 first work consisted in determining the proportion of nitrogen 

 present in a large number of feeding materials. Careful 

 practical trials were then made with a few selected foods, and 

 as a result he published a revised table of hay values, based on 

 the amount of nitrogen the foods contained, and checked to 

 some extent by his practical experience. His experiments led 

 Boussingault to bring into prominence the non-nitrogenous 

 constituents of food, but in general his conclusions were that 

 the comparative values of food-stuffs are determined rather by 

 their nitrogenous than by their non -nitrogenous constituents. 

 In this subject Boussingault's was the pioneer work, and 

 Liebig, who in many respects must be regarded as the 

 originator of any general theory of animal nutrition, in the 

 main arrived at his deductions from Boussingault's results. 

 Liebig also, and perhaps even more strongly than Boussingault, 

 looked at the nitrogenous matter as the most important 

 constituent of food for the production of both increase and of 

 work. 



In this position was the science of animal nutrition when 

 Lawes and Gilbert began their experiments on feeding, and 

 naturally the direction their experiments took was mainly 

 determined by the views then prevailing. The most notable 

 characteristic of the Rothamsted experiments on animals was 

 that from the first they were concerned with animals increasing 

 in weight rather than with animals whose food rations were 

 adjusted to maintain them in a constant condition. The 



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