THE SOURCE OF MUSCULAR ENERGY. 551 



4. An active muscle contains less extractives soluble in water, but, 

 on the other hand, more of those soluble in alcohol. It also contains less 

 of the substances that form carbon dioxid, less fatty acids, kreatin, krea- 

 tinin, and sarcophosphoric acid. 



5. During contraction the amount of water in muscular tissue is in- 

 creased, while that in the blood is correspondingly diminished. The 

 solid matters of the blood are increased, while those of the lymph (al- 

 bumin) are diminished. 



6. The question as to the extent to which the proteids of muscular 

 substance generate the kinetic energy of muscular activity, by the trans- 

 formation of their chemical potential energy, has been answered by 

 Pfliiger with the statement that albumin, if given in sufficiently large 

 amounts, may be the exclusive source of muscular force. 



This albumin represents a special variety, and is thought to be formed syn- 

 thetically from ordinary living albumin by the absorption of alcohol-radicals, 

 which may be withdrawn either from another proteid, or from fat and sugar 

 if there is a deficiency of proteids. The living albumin is transformed into a 

 readily decomposable, living proteid, which contains a greater amount of carbon, 

 and represents the immediate source of muscular energy. 



If a lean dog, fed only with lean meat and in a state of metabolic equilibrium 

 during muscular rest, is subjected to a period of several days' work, it must receive 

 a definite excess of lean meat in order to maintain its bodily weight. During the 

 period of activity, the animal, therefore, decomposes more proteid, in accordance 

 with the extent of the activity, and the metabolic equilibrium is thus maintained. 

 Undoubtedly the work performed is accomplished at the expense of an increased 

 consumption of proteids. If the dog does not receive an increased quantity of 

 proteids on beginning to work, it loses in bodily weight. 



Even though sufficient quantities of fat and carbohydrates, in addition to the 

 proteid, be administered to the active dog, there will still be an increased con- 

 sumption of proteids during work. 



As on administration of a sufficient amount of proteid the muscular work is 

 performed with the aid of this alone, and as in the decomposition of this proteid 

 neither fat nor carbohydrate results, the fat and carbohydrate cannot be the true 

 source of muscular force (Pfliiger) . 



The carbon dioxid resulting from the decomposition of proteid leaves the 

 body quickly through the pulmonary respiration; while the nitrogenous products 

 of decomposition are excreted slowly, even for as long as two days after the com- 

 pletion of the work. 



One and the same readily decomposable proteid is thus oxidized 

 slowly and continuously in the muscular tissue, with the generation of 

 heat, while under the influence of innervation it is consumed rapidly and 

 in larger amount, and is then the source not only of heat, but also of 

 kinetic energy. 



Pfliiger estimated that in his experimental dog one gram of nitrogen in the 



Sroteid, decomposed within the body, produced 7456 kilogrammeters of work. 

 f the total supply of energy contained in the proteid (measured by means of 

 the calorimeter in calories), the dog converted 48.7 per cent, into kinetic energy, 

 the remainder being transformed into heat. This 48.7 per cent, represents the 

 mechanical equivalent of the proteid. 



At an earlier period Fick and Wislicenus, as well as v. Voit and v. Pettenkofer, 

 had reached the conclusion as a result of their experiments that the daily 

 excretion of nitrogen is not increased to any considerable extent by forced work, 

 whereas the consumption of oxygen and the excretion of carbon dioxid are 

 increased, provided that the body' has at its disposal sufficient material containing 

 carbon, such as glycogen and fat, in its tissues or in the food. Hence, the proteid 

 cannot be the source of muscular energy. Increased elimination of nitrogen 

 takes place only when the activity gives rise to dyspnea, for deficiency in oxygen 

 causes decomposition of albuminates. 



Also the increased excretion of sulphuric acid resulting from work is indicative of 



