66 



PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



The laws for elastic changes in form of all bodies, including the soft 

 organic tissues, is expressed in the diagram given below (Pig. 44;. 



The 

 f the' 



The spaces on the line A 13 represent the extending weights, 

 spaces on the line B C represent the increase in length. Thus, i 

 extension of any given tissue by any given weight equal the ordinate, 

 A D, the increase in extending weight by regularly increasing amounts 

 will not produce a proportional increase in length. Each increase will 

 be less than that produced by the previous lesser extending weight, and 

 the line which connects the limits of extension will be a curve which 

 gradually tends to form a horizontal line— in other words, a hyperbola. 

 In a corresponding figure, representing the extension of an inorganic body, 

 the line D C, instead of being a curve, would be a straight line, and the 

 spaces on the line B C from B to C would be equal, showing that the 

 extension increases regularly with uniform increase in extending weight, 



with the exception above 



D 



alluded to, when very 

 great difference in ex- 

 tending weights is made 

 use of. This difference 

 between organic and in- 

 organic bodies is, without 

 doubt, attributable to the 

 greater extensibility of 

 the former. 



The organic tissues 

 have still another char- 

 acteristic which distin- 

 guishes them from the inorganic bodies, viz., when a tissue has been 

 extended by a weight, if the weight is allowed to remain the extension 

 gradually increases, and may not be complete for days or months ; this 

 is called elastic after-working. It is present in all elastic bodies, though 

 in rigid bodies it is much less marked, and its limit is sooner reached. 



The weight which will stretch a prism one square millimeter in area 

 and one meter long one meter, provided the limit of cohesion is not 

 thereby passed, is called the co-efficient of elasticity. 



The following figures, according to .Wundt, give the co-efficients of 

 elasticity of some of the more important organic tissues : — 



Bones, 2264. 



Tendons, . . ' 1.6693 



Nerves 1.0905 



Muscles, . 0.2734 



Arteries, 0.0726 



The smallness of these co-efficients is recognized when it is remembered 

 that for cast-steel it is 19881. 



