relations to various exigencies of the Animal Body. 57 



of muscular fibre, or, as it may be called, a rapid change of mat- 

 ter, determines a greater amount of mechanical force; and con- 

 versely, that a greater amount of mechanical motion (of mecha- 

 nical force expended in motion) determines a more rapid change 

 of matter." (Organic Chemistry in its applications to Physio- 

 logy and Pathology, 1842, pp. 220 & 221 .) 



And again : — 



u The amount of azotized food necessary to restore the equili- 

 brium between waste and supply is directly proportional to the 

 amount of tissues metamorphosed. 



" The amount of living matter, which in the body loses the con- 

 dition of life, is, in equal temperatures, directly proportional to 

 the mechanical effects produced in a given time. 



" The amount of tissue metamorphosed in a given time may 

 be measured by the quantity of nitrogen in the urine. 



" The sum of the mechanical effects produced in two indivi- 

 duals, in the same temperature, is proportional 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." 

 (Ibid. p. 245.) 



Our own direct experiments have had reference chiefly to the 

 feeding of fattening animals ; but the characteristic food require- 

 ments of the body, when fed with the view to the exercise of 

 muscular power, have also been made the subjects of inquiry. 



Referring to the feeding of fattening animals, the question 

 arises, whether in the use of the currently adopted food-stuffs 

 the amount of food consumed by a given weight of animal within a 

 given time, and the amount of increase produced are more influ- 

 enced by the amount of the nitrogenous or of the non-nitroge- 

 nous constituents which the food supplies; that is to say, 

 whether the sum of the requirements of the animal system 

 under these circumstances is such that, in the use of the ordi- 

 nary articles of food, the amount taken or increase produced will 

 be more regulated, or measurable, by the supplies of the nitroge- 

 nous or "flesh-forming" constituents, or by those of the more spe- 

 cially respiratory and fat-forming non-nitrogenous constituents. 



To acquire the data necessary for the satisfactory solution of 

 this question, some hundreds of animals — oxen, sheep, and pigs — 

 have been experimented upon. Comparative lots being selected, 

 the general plan of the feeding-experiments was to give to some 

 a fixed and limited amount of food of known composition in 

 regard to its contents of nitrogenous and non-nitrogenous con- 

 stituents, to others a fixed and limited amount of food of differ- 

 ent composition in this respect, and to allow all to take as much 

 as they chose to eat of some other food, also of known compo- 



