1892.] Heredity of Acquired Characters. 893 
bolic transformations of matter and energy, is admitted to be 
an essential condition of life in all tissues and elements of the 
body. 
As living matter the germ plasma must be continually 
undergoing metabolic changes in adjusting its internal rela- 
tions to its external relations with the body plasma, and inter- . 
changes of matter and energy must be involved in its increase 
and growth. 
These constant changes in the substance of the germ cells 
were not recognized in the original hypothesis of the contin- 
uity of the germ plasma. As formulated by Weismann 
“heredity is brought about by the transference from one 
generation to another of a substance with a definite chemical, and 
above all molecular constitution,” which he called germ plasma, 
and assumed that it possesses a “highly complex structure 
conferring upon it the power of developing into a complex 
organism,” and heredity was further explained, “ by suppos- 
ing that in each ontogeny a part of the specific germ plasma 
contained in the parent egg-cell, is not used up in the con- 
struction of the body of the offspring, but is preserved unchanged 
for the formation of the germ cells of the following generation.” 
Again he says, “the germ plasm, or idioplasm of the germ 
cell, (if this latter term be preferred), certainly possesses an 
exceedingly complex minute structure, but it is nevertheless a sub- 
stance of extreme stability, for it absorbs nourishment and grows 
enormously without the least change in its complex molecular 
structure.” It is difficult to understand how a living substance 
undergoing constant metabolic changes can be “a substance 
of extreme stability,” or how it can “grow enormously with- 
out the least change in its complex molecular structure. ” 
This assumed stability of molecular structure, and definite 
chemical composition of the germ cells appeared to be neces- 
sary to give plausibility to the claim of immortality, and the 
further assumption of the non-inheritance of acquired charac- 
ters. The transmission of a definite, stable, self-propagating 
substance from one generation to another, uninfluenced by the 
body plasma, has, in fact, been the shibboleth of those who 
deny the transmission of acquired characters, but Weismann 
