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 (Fig. 44). 



The spaces on the line A B represent the extending weights. The 

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

 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 bod}', 

 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, 

 A p with the exception above 



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. 



C 



FIG. 44. 



