304 HISTOLOGY OF THE MORBID PROCESSES. 



the cells of different tissues, being, roughly, inversely proportional 

 to the degree of specialization to which they have attained. Those 

 tissues whose functional activities in the adult are chiefly formative 

 possess this capacity for rejuvenescence in a high degree. In fact, 

 epithelium in many situations e. g., upon the skin merely requires 

 a little stimulation of its normal activities to produce new tissue. 

 The case is different with tissues of higher function, in which the 

 cells have become greatly specialized at a sacrifice of their formative 

 activities. In these the capacity for rejuvenescence is always com- 

 paratively slight, and may be entirely lost ; as, for example, in the 

 ganglion-cells of the central nervous system. Such parenchymatous 

 cells of high function are also more vulnerable than cells of a lower 

 type of specialization, because they are more dependent for their 

 functional activity upon a maintenance of the normal conditions of 

 nutrition. 



The foregoing considerations explain why the more highly spec- 

 ialized cells are damaged for a greater distance from the point of 

 injury than are the connective-tissue cells, and also why they play 

 a less prominent part in the restorative processes that follow those 

 which have been destructive. The result is that the zone of con- 

 nective tissue capable of rejuvenescence is nearer to the site of 

 injury than the zone which includes undegenerated cells of higher 

 function, and from this it follows that the defects in the tissues are 

 made good by a proliferation of connective tissue, accompanied in 

 only slight degree by a proliferation or restitution of the tissues of 

 greater specialization. The process of repair is more a patching 

 of the defect than a restoration of the normal structure. It results 

 in a permanent scar, and not the perfect replacement of lost tissues 

 by others of the same structure and function. 



During rejuvenescence the cells of the connective tissues enlarge 

 and become more cytoplasmic, and their nuclei become richer in 

 chromatin. They then divide by the indirect process, giving rise 

 to a number of spheroidal cells, which, together with newly devel- 

 oped loops of capillary bloodvessels, constitute an undifferentiated 

 tissue, called " granulation-tissue." During its formation at least a 

 part of the original fibrous intercellular substance appears to be re- 

 moved by absorption. This may be brought about by maceration in 

 the fluids present, or through the agency of the leucocytes that have 

 emigrated from the vessels and play the part of phagocytes (Fig. 269). 



The young vascular loops that supply the granulation-tissue are 



