.62 Messrs. J. B. Lawes and J. H. Gilbert on Food in its 



this most important field of inquiry if the prevailing opinions 

 on the subject were somewhat modified*." 



It will be borne in mind that at the time the statement of 

 view here quoted was made, the opinions expressed were directly 

 contrary to all recognized authority on the subject, and it is 

 since that date that so much evidence has been accumulated 

 in regard to the amounts of urea, and the amounts of carbonic 

 acid and other products, given off under varied conditions as to 

 food and exercise. Still, from the facts even then at command, it 

 was concluded that the increased demand for food resulting 

 from the exercise of muscular power was specially characterized 

 by the requirement for an enhanced amount of the non-nitroge- 

 nous constituents. Confirmatory evidence was, however, not 

 long wanting. 



In 1854 we selected two pigs as nearly as possible of equal 

 weight and character ; to one was given, ad libitum, lentil-meal 

 (containing about 4 per cent, of nitrogen) , and to the other, also ad 

 libitum, barley-meal (containing less than 2 per cent.). After the 

 animals had been kept for a certain time on their respective 

 foods, one comparative experiment was conducted for a period 

 of three days, and another for a period of ten days. The 

 weights of the animals were taken at the beginning and at the 

 end of each experiment, and, besides other particulars, the 

 amounts of nitrogen consumed in food, and voided as urea, 

 were determined j*. The result was, that with exactly equal 

 conditions as to exercise, both animals being in fact at rest, the 

 amount of urea passed by the one feeding on the highly nitro- 

 genous lentil-meal was more than twice as great as that passed 

 by the one fed on the barley-meal. We have since made other 

 such experiments with similar results. 



It was clear, therefore, that the rule laid down by Lieb'ig, 

 and assumed to be substantially correct by so many writers, did 

 riot hold good — namely, that " The sum of the mechanical effects 

 produced in two individuals, in the same temperature, is pro- 

 portional to the amount of nitrogen in their urine, whether the 

 mechanical force has been employed in voluntary or involuntary 

 motions, whether it has been consumed by the limbs or by the 

 heart and other viscera ■■ — unless, indeed, as has been assumed 

 by some experimenters, there is, with increased nitrogen in the 

 food, an increased amount of mechanical force employed in the 



* It is worthy of remark, too, that neither are the most highly nitroge- 

 nous wheats the most valued by the baker for the purpose of bread-making, 

 nor is the most highly nitrogenous bread the most valued by the chiefly bread- 

 fed working man. See " On some Points in the Composition of Wheat- 

 grain, its Products in the Mill, and Bread," Journ. Chem. Soc. vol. x. 1858. 



f Phil. Trans, part 2, 1859, p. 554. 



