( 45 ) 



The determination of hardness may give absolute and relative 

 values. Among the methods of relative determination that of Thoulet 1 ) 

 appeared to be useful also to delermine the relative hardness of 

 living objects. 



Thoulet examined the elasticity of rocks and found points of 

 comparison for this in the number of reflections and in the angle of 

 reflection of a swinging ball suspended in the air. Indeed, if we 

 drop a hard, elastic object upon an other, it will among others 

 depend on the hardness of the surface that is hit, how often and 

 how far the reflection will take place. Now, if this principle is put 

 into practice with a much weaker object like a muscle, these reflec- 

 tions will, though in a smaller degree, yet take place in the same 

 manner, which is corroborated by experience. 



The angle of reflection of a falling globule resp. the number of 

 its perceptible taps or reflections depends: 



1. on the cohesion, elasticity and plasticity of the falling globule. 



2. on the cohesion, elasticity and plasticity of the object hit, in 

 this case the muscle. 



Now as in case of comparing determinations sub 1 remains constant, 

 sub 2 must be the only changeable, determinative factor. 



The investigation takes place as follows with an apparatus that I 

 call physiological sclerometer. 



Physiological Sclerometer. Schematic drawing. 

 Fig. 1. 



J ) M. J. Thoulet. Recherches sur l'élasticité des mineraux et des roches. Goniptes 

 rendues de 1' Academie des sciences. Paris. Tome 96. 1883. 



