NATURE OF IRRITATION AND EXCITATION. 165 



as it were, but of course very slowly, the dead bone, 

 which soon becomes surrounded by them. After the 

 bioplasts have accumulated to a certain extent, many 

 increase in size, produce formed material, which in 

 its turn ossifies, and thus the piece of dead bone is at 

 length imbedded in new irregularly formed bone. 

 This process goes on, unless the whole of the dead 

 bone (sequestrum) is removed by the process above 

 referred to, or by surgical interference. Before the 

 dead bone can be removed by the surgeon, he has in 

 many cases to cut away very much of the new bone 

 which has been produced. Now, it has been said 

 that the dead bone acts as an irritant as a foreign 

 body and that this is 'the reason why the bone in- 

 creases around it. Such a doctrine is still strongly 

 maintained, although no one has been able to show 

 .exactly what is meant by the supposed "irritation." 



225. Nature of irritation and excitation. It has 

 been assumed that an irritant or excitant is always 

 necessary to increased action, that by this " irritant " 

 the living cells are " excited " to live faster than usual. 

 For this increased activity, all that is really re- 

 quired is a more free access of nutrient matter. The 

 so-called " irritant," instead of " exciting," acts in 

 the most passive manner possible. It permits pabulum 

 to have freer access to the living bioplasm. By it the 

 restrictions under which growth normally takes place 

 are to some extent removed. There is no " excita- 

 tion to increased action " at all. The more freely 

 living matter is supplied with pabulum, the faster it 

 grows. "Increased action" in a living structure 

 results from the removal of restrictions, as occurs when 

 the rupture, perforation or softening of the " cell- wall " 

 or "intercellular substance," takes place. The 

 nutrient pabulum comes more readily into contact 

 with the bioplasm which grows faster, but not in 

 consequence of "stimulation," "excitation," or "irri- 

 tation." 



