BIOLOGY. 289 



gi'oups, — carbonaceous or non-nitrogenous, such as fat, starch, 

 sugar ; and the nitrogenous, such as fibrin, albumen, and casein, — 

 the former class being regarded as compi'ising simple heat-givers, 

 that is to say, substances that furnish material for oxidation in the 

 process of respiration, and thus maintain the temperature of the 

 body; the nitrogenous constituents being the flesh-formers, or 

 substances building up the muscles of the body, through which 

 motive force is exerted. The exercise of a muscle being accom- 

 panied by a proi)ortionate destruction or oxidation of its tissue, it 

 follows that the plastic or flesh-forming constituents of food should 

 bear a relation to the amount of muscular work performed. This 

 theory, namely, that mechanical work, i. e., muscular exertion, is 

 dependent on the destruction of muscular tissue, has been sup- 

 ported by Ranke, Playfair, Draper, and others ; and, as we have 

 already stated, it has been generally taught up to the present 

 time. Nevertheless, it has not escaped challenge. Immediately 

 after its promulgation. Dr. J. R. Mayer wrote, " A muscle is only 

 an apparatus by means of which the transformation of force is 

 effected, but it is not the material by the chemical change of which 

 mechanical work is produced." This assertion he supported by 

 several cogent arguments. Other physiologists also expressed 

 similar opinions. Messrs. Lawes and Gilbert advocated a like 

 view, basing their opinions on their own elaborate and carefully- 

 executed experiments on the feeding of cattle. 



Some very important researches upon this subject have been 

 recently published by Drs. Fick and Wislicenus, Professors at the 

 University of Zurich, and also by Dr. Frankland in London. An 

 account of these experiments was given in a lecture delivered at 

 the Royal Institution by the latter chemist during last session. 



It is probable that these investigations Avill very materially 

 affect the present condition of physiological science, tending, as 

 they do, to entirely change the ideas hitherto entertained respect- 

 ing the relation of food to the requirements of the animal body. 



The question is to determine whether the muscle is merely the 

 apjjaratus by which animal motion is jiroduced, or whether it fur- 

 nishes both the ajaparatus and the force to work it. In order to 

 solve this problem by experiment, there are three things neces- 

 sai-y to be determined. First, the amount of force or energy 

 generated by the oxidation of a given amount of muscle in the 

 body ; secondly, the amount of mechanical force exercised by the 

 muscles of the body during a given time ; thirdly, the quantity of 

 muscle oxidized in the body during the same time. 



It follows that if the amount of mechanical force exercised by 

 the muscles be greater than the amount of the substance oxidized 

 could furnish, the force of the muscles is not exclusively derived 

 from their own substance. When muscle is consumed in the bodj^ 

 its nitrogen appears principally in the form of urea. Hence the 

 amount of energy derived from the oxidation of muscle in the 

 body will be expressed by the heat of combustion of the muscle 

 itself, minus the heat of combustion of that amount of urea which 

 the muscle would furnish when consumed in the body. Tliis dif- 

 ference of heat was determined by Frankland, who found that to 

 25 



