234 
G. Uciny Yule. 
for Haemoglobin, C 75S H 1 203 O 21S N 195 S ;5 Fe, the first 
containing 2716 atoms, the second 2378. I confess I speak without 
a knowledge of modern chemistry, but I can see no physical reason 
why the loss of an atom or two of hydrogen, or of carbon, in any 
such case should entail so great an alteration of structure in the 
molecule as to alter completely its physical and chemical characters. 
It does not seem wholly absurd to suggest that one might obtain 
within limits a sensibly continuous variation of properties with 
such a compound, even supposing it possible to isolate “ pure 
cultures ” of identically similar molecules. “ Continuous variation ” 
would then correspond to such minor alterations as did not destroy 
the stability of the general structure, “discontinuous” or abnormally 
large variations to such alterations as caused the whole structure 
to slide over, so to speak, into a new position of equilibrium. I 
write with a picture in my mind of Mr. Galton’s model :—an 
irregularly polygonal prism which is stable about its position of 
rest on one face for small oscillations, but will fall into a fresh 
position if the oscillation be too great (Bibliography, 2 ). 
So far then as speculative possibilities go, the occurrence of 
sensibly continuous variation in the properties of an isolated 
“determinant” seems a hypothesis by no means to be excluded, 
and surely it can be put to the test. Mr. Bateson appears to 
accept, and Mendel’s hypothesis almost to imply, the truth of the 
theory of the continuity of the germ plasm as distinct from a theory 
of pangenesis. If then the individual variations of a character are 
heritable, it follows that they are, in part at least, due to germinal 
variation and not wholly to circumstance; if the character is one 
obeying Mendel’s Laws, it also follows, with a high degree of 
probability, that it is represented by a single determinant, and 
therefore if the individual variations are heritable, variations in 
the single determinant are possible. Such an experiment is surely 
necessary to clear up the facts. 
But further, all characters cannot be simple units. To take 
the simplest possible case of compounding, let x x x' x be a pair of 
corresponding lengths (say) in two races, these lengths obeying the 
laws of dominance and segregation ; and let x 2 x' 2 be another pair 
pair of corresponding lengths also obeying the laws. Then clearly 
Mendel’s Laws cannot hold for the “ compound characters ” 
X = x x + x 2 
X' = x\ -f- x' 2 
If x x and x 2 be both dominant with respect to x\ and x'. 2 then the 
