THE HUMAN STRUCTURE 



101 





It is clear from these figures that the structure ol the material 

 has the chief influence on its elastic properties and density. 



But it must be noticed that the viscous nature of the muscles 

 and the tendons renders them liable to deformations. Their 

 elasticity, which mitigates the effects of shocks, can be fatigued, 

 for example, by walking or running. Thick organs have only a 

 small retardment of elasticity (elastiche nachwirkung) . This 

 has been noticed with thick rods of indiarubber, and is a feature 

 which distinguishes the muscles of athletes. 



Elasticity shows itself most in the fundamental organs, of life, 

 circulatory and respiratory, and assures efficacious protection 

 and regular working ( 49). ( 4 ) It shows itself less in the skeleton, 

 where its greatest value is found in the ribs. Above all, it is a 

 function of age, its properties in man being at their best between 

 20 and 40 years of age, though the suppleness of the tissues is 

 much greater at an earlier age. It is utilised during physiological 

 work, and it repairs itself in repose, depending on the method of 

 " alimintation/' and on the nature of the activity of the subject. 

 Adaptation and activity, in part, contribute to the elastic 

 accommodation of the muscles. Abnormal efforts, such as rapid 

 movements, tend to deform the tissues permanently, and even to 

 break them when, in old age, their tenacity has weakened. Also, 

 the persistance of the deformation, (such as the contraction of the 

 planar arch of the feet after a fatiguing walk) ( 5 ) is accompanied 

 by a diminution, if not a momentary arrest of human activity, 

 and causes acute discomfort. 



(*) Young's modulus varies with the elognation, fromE = 0'07 to E = 15. 

 For ordinary limits of elongation, E = 0'09 (Villari, Pogg. Ann., vol. 

 cxliii., 1871). 



( 2 ) Bouasse, Heim, etc. The value R is for vulcanised rubber. 



() Benton, in The American Journal of Science, 1907, p. 75. 



(*) Buttersack, Die Elasticitat, eine Grundfunktion das Lebens, Stuttgart, 

 1910. 



(*) Dew&vre (Comptes Rendus Biologie, 1892 ; Mimoive, p. 207). 



