Analysis of Rate of Regeneration 415 
that the curve of rate of regeneration most closely resembles the 
curve of growth. In each the rapid decline from the highest 
point becomes more gradual as the curve approaches the base 
line, that is the rates at which growth and regeneration proceed 
decrease less rapidly as they approach their completion. Minot 
recognizes two factors controlling the rate of growth: (1) The 
tendency of undifferentiated cells to multiply; (2) the tendency 
of undifferentiated cells to differentiate into cells that do not 
multiply. The former is preponderant when the rate is high, 
the latter begins to influence the rate when it is at the maximum, 
and increases in its effect until it entirely overcomes the animal’s 
power to grow. 
The general similarity in the course of change in the rate of 
regeneration and the rate of growth, probably means that there 
is at least a general likeness in the factors controlling the two 
processes. 
There are two possible explanations for the low rate in the ini- 
tial interval of regeneration: (1) It may be that the shock given 
the animals by the operation makes them too weak to begin 
regeneration at once; (2) It may be that some time is consumed 
immediately after the operation in the formation of an embry- 
onic tissue which serves as a basis for subsequent regeneration. 
The exact nature of the shock incident to such an operation, and 
its effect upon the tadpoles, can only be conjectured. It probably 
includes: (1) Certain local effects, as a bruising of the flesh on 
the line of operation, and the irritation of the cut by the water or 
by micro-organisms in the water; (2) Constitutional effects, as the 
loss of blood, the nervous shock due to pain inflicted by cutting 
the central nerve cord, and the waste of muscular energy, con- 
sumed in violent attempts to swim with the stump of a tail, to 
which the animal is not accustomed. ‘The last two suppositions 
have nothing better to substantiate them than the actions of the 
tadpoles during and following the operation. When they are 
being measured tadpoles will not lie in one position for more than 
a fewseconds. The operation causes them to give a sudden start, 
after which they lie relaxed and motionless for from twenty to 
thirty seconds. However, when they are placed in a dish of water 
