178 



VUCI1£RIX.\R\- PAIIIOLOUW 



kidney. The law of specificity, i. e., cells beget like cells, is 

 the same in regeneration and in ph_vsiologic processes. Regen- 

 eration is the outcome of the unhindered multiplication of cells. 



Blood is continually regenerated during the natural life of an 

 animal. The normal maintenance of blood is a physiologic pro- 

 cess, but regeneration of blood or some of its constituents may, 

 under certain conditions, be al^normal, as in leukemia. Leuco- 

 cytes are produced in lymphoid tissue of the lymph nodes, spleen 

 and bone marrow, and it is possible that they may multiply in 

 the tissue spaces. Erythrocytes probably have their origin in the 

 red marrow of l)ones in adult animals. The red blood corpuscles 

 are nucleated in the beginning but the nucleus vanishes by so- 

 lution or extrusion before the cells reach the general circulation 

 except in case of severe hemorrhage or other conditions in 

 which there has been rapid, extensive loss or destruction of 

 blood. 



Blood vessels are usualh- the first tissue regenerated in the 

 repair of wounds. Blood vessels are formed in the embryo by 

 canalization of large mesodermal cells, many of which fuse, thus 

 forming continuous canals that later become blood vessels. This 



Vasnilar Regeneration, showing vascular buds. 



type of \-ascular formation is not common in repair of injured 

 vessels r.r regeneration n{ destroyed vessels. The usual manner 

 of vascular regeneraticjn is by the growth and development of 

 endothelial buds from adjacent vessels. These buds are solid, 

 cdnical iiroces-^es which extend outward from the capillary en- 

 dothelium, Tlie buds or processes increase in size and become 

 hollow at their base, the cavity beino- thus continuous with the 

 br.nen <>{ the pre-existing vessel. .\s the buds increase in size 



