336 THE CHEMISTRY OF PROLIFERATION 



sidered, and, better still, if these mitotic divisions 

 are actually seen as they occur in response to chemical 

 agents, it will be appreciated that there is a strong 

 probability that cells only divide when they are made 

 to do so by an exciter of reproduction. 



The active auxetics are contained in "the remains 

 of dead tissues." Globin is in reality "the remains of a 

 dead tissue," for it is obtained by the decomposition 

 of haemoglobin, and haemoglobin is contained normally 

 in living red cells. Doubtless the constituents of the 

 molecules of kreatin, xanthin, and the active principle 

 of globin are present in living protoplasm; but they 

 may not be present, presumably, in the same combina- 

 tion or form as they exist in kreatin and xanthin. 

 Possibly it is only after death that these substances 

 are produced, in which case it would follow that a cell 

 will not reproduce itself by virtue of the constituents 

 of its own living protoplasm; but it is necessary for it 

 to absorb fresh active agents from the dead remains of 

 its' neighbours. 



Many points are now explained. When it is re- 

 quired that an indolent healing surface shall heal well, 

 we scarify it, as exemplified in the operation of Thiersch 

 grafting. If a fractured bone will not unite, the ends 

 are rubbed together or actually "freshened" by opera- 

 tion, to produce callus; and callus is really a tissue 

 made by the proliferation of cells. When we scarify 

 or freshen a surface, we merely cause destruction, and 

 thereby set free exciters of reproduction. If a part of 

 the body is bruised, haemorrhage occurs; and, as is 

 shown by the pigmentation, the haemoglobin set free 



