Maboh 29, 1907] 



SCIENCE 



4M 



phragm, etc., are endowed, are very abun- 

 dant, and exceed by far the needs for the 

 activities of normal life. The mechanisms 

 of many functions are doubled and trebled 

 to insure the prompt working of the func- 

 tion. In many cases the function of one 

 organ is assured by the ready assistance 

 offered by other organs. The continuance 

 of the factors of safety is again protected 

 by the mechanisms of self-repair peculiar 

 to the living organism. We may then 

 safely state that the structural provisions 

 of the living organism are not built on the 

 principle of economy. On the contrary, 

 the superabundance of tissues and mechan- 

 isms indicates clearly that safety is the 

 goal of the animal organism. We may 

 safely state that the living animal organ- 

 ism is provided in its structures with 

 factors of safety at least as abundantly as 

 any human-made machine. 



The safety of a mechanism is increased, 

 as we have stated before, also by an eco- 

 nomic handling of the expenditure of its 

 energy. The expenditure of energy by the 

 living animal organism consists chiefly in 

 the work which it performs, that is the 

 contractions of the muscles. Of the in- 

 voluntary work of the body it is only the 

 action of the heart and the respiratory 

 muscles of which we possess a knowledge of 

 some available facts. The heart, although 

 capable of doing a great amount of work, 

 is normally kept down to perform only the 

 most indispensable duty. The inhibitory 

 tonus exercised by the vagi prevents the 

 heart from beating too rapidly and too 

 strongly, when it is not required; and the 

 vascular reflexes carried from the heart or 

 aorta to the vasomotor centers regulate the 

 vascular circulation so as not to offer too 

 much resistance on the one hand, and not 

 to fiU up the heart with too much blood on 

 the other hand. 



The respiration is normally carried out 

 only by one muscle, the diaphragm, and 



this works only with a fraction of its 

 capacity, the distention of the lungs pro- 

 ducing an inhibitory stimulus preventing 

 the muscle from overaction. 



The contractions of the skeletal muscles 

 being regulated chiefly by the will, offer 

 insufficient opportunities for a study of the 

 normal regulation of expenditure of energy 

 emanating from this source. There are, 

 however, two facts which are instructive 

 and deserve to be mentioned. One is the 

 provision of the muscle with the sense of 

 fatigue setting in with overexertion; it 

 might serve as a guard against overwork, 

 against exhaustion of the muscles. The 

 second fact is the provision of the muscular 

 innervation with inhibitory impulses for 

 antagonistic muscles; it prevents harmful 

 or even only unnecessary contractions. In 

 other words, it prevents the muscles from 

 an unnecessary expenditure of energy. 



While the facts are not many, they are 

 sufficient to indicate the tendency of the 

 organism to be economical in its expendi- 

 ture of energy. 



We now arrive at the examination of the 

 principles of governing the supply of the 

 organism with energy. A machine is pro- 

 vided with fuel far above the^ necessity for 

 the performance of the expected minimum 

 work; it has to be in readiness for unfore- 

 seen exigencies. How about the organism ? 

 The supplies for the animal machine con- 

 sist of inorganic salts, water, oxygen and 

 food. Our knowledge of the laws govern- 

 ing the supply and expenditure of water 

 and inorganic salts for the animal or- 

 ganism are still too imperfect to be utilized 

 here for the elucidation of our problem. 

 We have to restrict our discussion to the 

 supply of food and oxygen. The supply 

 of food is influenced so much by the will 

 of the animal that it is difficult to obtain 

 facts permitting only one interpretation. 

 For instance, the amounts of food taken 

 by men in all parts of the world can not 



