34 J. WILLIAM BUCHANAN 
on head frequency are almost invariably different in pieces from 
these regions, and regard the B pieces as representing intermediate 
conditions. 
The conception of specific formative substances as determining 
factors in regeneration advanced by Sachs and offered by Mor- 
gan, Loeb, and others (see, for example, Morgan, '05, and Loeb, 
'16, p. 155) may be dismissed with brief consideration. If a 
head-forming substance is a chemical entity, it must follow the 
laws of chemical and physical reactions when acted upon by some 
external agent. According to the law of mass action, one must 
assume that it should be acted upon by the agent in the same 
manner in both A and C pieces. In event of either complete 
or incomplete reaction between the external agent and the sub- 
stance, destruction or inhibition of the substance should take 
place in both A and C pieces. In other words, if head formation 
depends on the amount of head-forming substance present, 
head frequency should be decreased in both A and C pieces if 
the pieces are exposed to an agent under conditions of time and 
concentration that inhibit head formation. But the evidence 
presented here that anesthetics decrease head frequency in A 
pieces and increase it in C pieces under identical conditions of 
time of exposure and concentration is unmistakable, and KNC 
has been shown to have a similar effect. These results make it 
impossible to explain head determination on the basis of any 
specific head-forming substance. 
Attempting to explain the experimental results on the basis 
of the amount of nutritive materials present in the two regions, 
leads us into a similar conflict with the law of mass action. It 
is inconceivable that the anesthetics destroy nutritive materials 
in the A pieces and elaborate them in the C pieces; or that they 
prevent the utilization of such materials in the A pieces and facili- 
tate these processes in the C pieces. 
The idea of a possible different specific action of the anes- 
thetics on the development of the tissues of the A and C pieces 
is next to be considered. In general, the same body tissues, body 
wall, muscles, gut, nerves, etc., are present in both regions, 
although probably in different amounts. The processes in- 
