Amount of Tail Regenerated to Removed in Tadpoles 443 
it showed the effect of extremely severe injury upon the rate of | 
regeneration. ‘he rate of regeneration of these four was lower 
than that of the Series R (10 mm.); this fact is probably to be 
accounted for by the effect or shock of the extreme injury. No 
conclusion, however, can be reached from these four animals alone. 
Another interesting relation between the level of injury, and 
regeneration, is noticed in the length of the first period of regenera- 
tion, the one of low rate, in all of the experiments. This period is 
longer the higher the level of injury, that is, the greater the amount 
removed. It does not, however, increase proportionally with the 
level of injury. ‘This difference in the length of this first period of 
regeneration may be due to one or both of two things: (1) The 
direct effect of the injury itself, that is, the shock of injury 
occasioned by the sudden loss of a quantity of blood and the over- 
stimulation of the nervous system; that is, the sudden appearance 
of the abnormal factor, injury, in normal life; or (2) the delay 
due to the healing over of the surface of the wound. Either of 
these would prolong this first period of slow regeneration; the 
former, since the amount of injury, that is, the absolute amount of 
tissue removed, varies with the level of injury; the latter, since the 
area of the cross-section of the tail, hence the area to be healed over, 
varies with the level of injury. Data were not collected from which 
conclusions could be drawn concerning this point, but the histolog- 
ical investigations of Durbin on the early stages of regeneration of 
the tadpole, show the latter to be the more probable. 
The following conclusions are taken from the data collected: 
1 The level of injury first producing death was 20 mm: cepha- 
lad from the tip of the tail, tail length 26 mm. 
_ 2. The rate of regeneration varies as the level of injury until the 
20 mm. level is reached. 
3. The first slow period of regeneration increases in length the 
higher the level of injury. 
Relation of the Amount Regenerated to the Amount Removed 
In both the experiment which suggested these investigations, and 
Experiment I, it was noted that the amount regenerated at the 
end of twelve days after the operation, varied directly, that is, 
