320 THE ANIMAL AS A PRIME MOVER. 



genie matter, and later investigation has shown that glycosie matter is 

 distributed throughout the animal system from the liver and through 

 the circulatory system into the capillaries, where it largely disappears 

 and carbon dioxide comes into view. It is now well understood that 

 the oxidations and the energy transformations essential to animal life 

 and activities occur through reactions between the oxygen in solution 

 in the blood of the arteries and the combustible elements accompanying- 

 it, which chemical operations take place in the depths of the tissue cells, 

 and, perhaps, in the capillary vessels. It is also now admitted that the 

 quantity of action is probably proportional to the loss of sugar and of 

 oxygen, and to carbonic acid replacing the lost glycose as a product of 

 its oxidation. 1 Since these chemical combinations are invariably low- 

 temperature combustions, and since they are vastly greater in quantity 

 in the active than in the passive muscle, and since the heat ultimately 

 derived is the excretum of the system and the final result of energy 

 transformation, it may fairly be concluded that an intermediate trans- 

 formation, or series of transformations, as yet unidentified, either quali- 

 tatively or quantitatively, constitutes the physiological method of pro- 

 duction of work. Glycosie substance is not found concentrated in any 

 considerable quantity in the tissues, except in the liver, the organ in 

 which it originates, and the only conclusion would seem to be that 

 glycogenesis is the one extremity of a chain of transformations, of which 

 heat constitutes the other. In this sense the hepatic gland is the source 

 of muscular power as well as of animal heat. It is this fact which makes 

 the flow of blood to the working part, and the volume of its channels, 

 measures of the energy there applied. 2 The weight of blood flowing 

 through a muscle at work was found by Chauveau and Kaufmann to be 

 about 85 per cent of the weight of the muscle itself, each minute of 

 working time, for full load. Its amount varies with the work performed, 

 external and internal. The circulation, with the muscle in repose, was 

 found by the same investigators to be about one-fifth as great as when 

 full work. The succession of changes is thus, probably, as follows: 



(1) Potential energy in foods is rendered available as a source of 

 kinetic energy by change of the foods into the various constituents of 

 the blood by chemical action and the expenditure of some probably 

 small net amount of chemical energy. 



(2) This available potential energy is transferred to the capillaries 

 by the blood, and its elements are selected by each organ for its own 

 special development of mechanical work or of other and active energies. 



(3) Chemical combinations take place, resulting in the production of 

 active forms of energy, applicable to the special work of the organ, as 

 mechanical work in the muscle, chemical action of characteristic kinds 

 in the glands, nerve power in the nervous system, and the accessories 

 of thought in the brain. 



1 See Chauveau and Kaufmann. Comptes rendus, T. CHI, 1886. 



2 Chauveau and Kaufmann. Comptes rendus, T. CIV, 1887. 



