30 PRINCIPLES OF VETERINARY SURGERY 



The regeneration of heart muscle is very limited; wounds 

 practically always heal by means of connective-tissue scars, 

 and the continuity of the contractile substance is never re- 

 stored. Involuntary muscle may be reproduced to some de- 

 gree after traumatic and other necroses; but wounds in the 

 alimentary and urinary tracts are largely healed by scar- 

 tissue. In the muscular layer of the uterus, where the organ 

 increases in size from ten to twenty times during pregnancy, 

 there are very few new muscle-fibres formed, but the indi- 

 vidual fibres undergo a marked increase in size, — hyper- 

 trophy. These are normally about i-iooo to 1^500 of an inch 

 in length, while during pregnancy their length increases 

 from 1-25 to 1-75 of an inch. There is also a corresponding 

 increase in the width. The blood vessels also show an in- 

 crease in the size of their muscle fibres. 



Some animals possess a more marked degree of muscle 

 regeneration than others. In man this occurs only after, a 

 slight injury of the muscle. In the horse, complete and very 

 extensive atrophies may manifest a marked tendency to re- 

 generate and resume their normal constitution and function. 

 The process is generally slow but it is certain. Examples 

 are found in the crural atrophy of azoturia and the should- 

 der atrophy of "shoulder-slip" so-called. 



NERVOUS TISSUE.— The peripheral nerves are cap- 

 able of extensive regeneration. When a nerve is divided, it 

 is invariably followed at once by degeneration of the entire 

 peripheral segment and of a variable portion of the central 

 segment, sometimes as far as the sixth node of Ranvier. 

 Not infrequently single fibres degenerate for long distances 

 toward the centre, even though surrounded by intact fibres. 

 This degeneration is characterized by disintegration of the 

 axis-cylinder and medullary sheath. The axis-cylinder first 

 swells up, presenting small villous dilations along its sides, 

 and these break up into small fragments. Secondarily, the 



