22 PRINCIPLES OF VETERINARY SURGERY 



largely composed of small round cells, the youngest form of 

 connective tissue cells. 



REGENERATION OF THE INDIVIDUAL 

 TISSUES. 



One law holds good for the regeneration of every kind of 

 tissue. "Omnis cellula e celkila ejusdem generis." This law 

 was first formulated by Bard and is universally applicable. 

 Muscle is formed from pre-existing muscle-cells, but it can- 

 not produce nerve. In the same way connective tissue will 

 produce any of its own varieties, but it never becomes epithe- 

 lium, and vice versa. 



The blood-vessels are almost the first to regenerate, for 

 if the new tissue forming is not nourished, it will soon de- 

 generate. The endothelial cells of the old capillaries send out 

 protoplasmic processes into the surrounding tissues. These 

 processes meet and unite into endothelial tubes which even- 

 tually become hollowed out as the blood begins to circulate 

 and push its way through the capillary system. The vessels 

 probably acquire their adventitia from the adjacent connec- 

 tive tissues, but the origin of their muscle fibres is not defi- 

 nitely known. 



CONNECTIVE TISSUE.— The regeneration of con- 

 nective tissue is by far the most frequent in the body, for it 

 enters into the organization of every kind of tissue that has 

 become useless or destroyed. Its proliferation occurs not 

 only in replacing connective tissue, but in replacing tissues 

 and organs- which have not, the power of reproducing their 

 own specific cells. It occurs also as a secondary process after 

 a number of inflammatory conditions. It is characteristic 

 of old age. If the parenchymatous organs of old animals, the 

 liver, kidney or spleen, and also the heart are examined mi- 

 croscopically, they will be seen to contain a large amount 

 of connective tissue. In animals that have been worked in 



