THE ANIMAL AS A PRIME MOVER. 313 



PART II.— ENERGY SUPPLIED; POWER AND EFFICIENCY; INTERNAL 

 WORK OF THE VITAL MACHINE. 



The energy expended by the vital machine consists of: 



(1) The external work performed, as the task of the workingman. 



(2) The external work performed incidentally outside of that useful 

 work, as- in the movements of the limbs, walking, handling the food, 

 and various voluntary and other motions, which constitute a consider- 

 able fraction of the more or less necessary expenditure of energy in 

 ways not included in the daily specified task. 



(3) The internal work of digestion, assimilation, nutrition, and rejec- 

 tion of excreta. 



(4) The interna] work of respiration. 



(5) The internal work of circulation of the blood and the other fluids 

 of the system. 



(6) The internal work of growth, maintenance, reconstruction, and 

 repair. 



(7) The internal work of the automatic system regulating the func- 

 tions and movements of the various organs, both external and internal. 



(8) The internal work of conscious direction of the movements of 

 body and limbs, and, in some cases, of internal organs, and, to some 

 extent, of the work of respiration and of circulation. 



(9) The internal work of the brain, and possibly of other organs, in 

 the performance of conscious thought and of brain work, a large part 

 of which is essential to the proper performance of the useful work of 

 the vital prime motor, and in the case of the man whose duties are 

 those, distinctively, of the thinker, a large part of which must be rated 

 as useful and prescribed work, determining the efficiency of the machine. 



(10) Peculiar and characteristic forms of energy which are the special 

 produce of some organism or class of organisms, and not essential ele- 

 ments of its operation as a vital machine, but which are employed 

 occasionally as the special provocation to which they respond comes 

 into action. 



Such is the internal work last mentioned — that of the brain — where 

 it is not the useful product of the machine ; such is the energy expended 

 in the production of the poison of the serpent, the secretion of offen- 

 sively odorous fluids in many animals and, perhaps, the honey produc- 

 ing glands of the bee maybe thus classed. The most remarkable, and, 

 in this connection most important, illustrations of this class, are found 

 in the generation and use of the electric fluid by the torpedo and gym- 

 notus and the production of light by the glowworm and firefly. 



Hibernating animals exhibit a peculiar modification of the action of 

 the vital fuuctious; their whole purpose, during hibernation, being to 

 insure of the continuance of the physical operations of circulation and 

 respiration by the employment of the previously stored energy of the 

 accumulated fat of the body. Very little tissue is wasted or repaired, 

 and the whole system is simply preserved in action through a period of 



