CHAPTER VI 



REGENERATION OF INTERNAL ORGANS. HYPERTROPHY. 



ATROPHY 



IT is a more or less arbitrary distinction to speak of internal in 

 contrast to external organs, since the latter contain internal parts ; but 

 the distinction is, for our present purposes, a useful one, especially in 

 regard to the question of regeneration and liability to injury. In this 

 connection we shall find it particularly instructive to examine those 

 cases of regeneration of internal organs that cannot be injured, under 

 natural conditions, without the animal itself being destroyed. An 

 illustration of this may be given. The liver, or the kidney, or the 

 brain of a vertebrate can seldom be exposed to accidental injury with- 

 out the entire animal being destroyed, although, of course, diseases 

 of various kinds may injure these organs without destroying the ani- 

 mal, but cases of the latter kind are not common. 



The experiments made by Ponfick ('90) on the regeneration of the 

 liver in dogs and in rabbits gave the most striking results. Ponfick 

 found after removal of a fourth, or of a half, or even, in a few success- 

 ful operations, of three-fourths of the liver, that, in the course of four 

 or five weeks, the volume of the remaining part increased, and in the 

 most extreme case, to three times that of the piece that had been 

 left in the body. The first changes were found to have begun as 

 early as thirty hours after the operation, when the liver cells had 

 begun to divide. The maximum number of dividing cells was found 

 about the seventh day, and then decreased from the twentieth to the 

 twenty-fifth day, but cells were found dividing even on the thirtieth 

 day. These dividing cells appeared everywhere throughout the liver, 

 and were no more abundant at the cut-edges than elsewhere. There 

 takes place, in consequence, an increase in the volume of the liver, 

 rather than a replacement of the part that is removed. The increase 

 takes place in the cells of the old part, the lobules swelling up to two, 

 three, or even four times their former size. No new liver lobules 

 seem *:o be formed. The old tubules of the liver also becom-; larger, 

 owing to an increase in the number of their cells. Since the change 

 takes pl.ace in the old part, and is due to an increase in size of the 



