474. 
the germ in multicellular organisms is less 
readily influenced by environmental influences 
than the soma; profound somatic modifications 
may leave the germ-plasm apparently un- 
affected. There is, however, nothing surpris- 
ing in this when it is considered that the un- 
developed germ forms in most cases only a 
small and inaccessible part of the total organ- 
ism; it is usually not subjected to external 
influences until it separates from the parent 
and begins its own independent development. 
But after this has happened environmental 
conditions may affect the egg and developing 
embryo just as they affect the adult, and the 
normal course of development may then be 
experimentally modified; e. g., cyclopia may be 
produced in fish embryos, ete. No one can say 
at what time the protoplasm of the developing 
germ, whether in the one-celled or many-celled 
stage, ceases to be germ-plasm and becomes 
somatoplasm. Just as the rigid distinction be- 
tween germ and soma can not be maintained, 
so it is doubtful if the “ hereditary material ” 
ean be identified with any special single struc- 
tures or cell-constituents, such as the chro- 
matin. A universal peculiarity of the cellular 
type of organization appears to be that the 
nucleus, which always contains chromatin 
among other constituents, is indispensable to 
the continued normal physiological activities 
of the cell, including those specific synthetic 
processes of which growth and heredity are 
the most evident expressions. But to regard 
protoplasm (somatoplasm) as the expression 
and chromatin as the seat of heredity (p. 93) 
does not seem justifiable on physiological 
grounds. In the specific constructive processes 
which determine the course of development 
the physiological activity of the entire cell is 
eoncerned. To say this, however, is not to 
deny that there may be a functional differen- 
tiation, corresponding to the chemical and 
structural differentiation, among the various 
cell-constituents; and that a special sienifi- 
cance in relation to the specific syntheses in- 
volved in development may: attach to the 
nucleoproteins of the cell-nuclei, z. e., to the 
chromatin. It is more consistent with mod- 
ern physiology to conceive of chromatin as an 
SCIENCE 
* [N. 8. Vou. XLVIII. No. 1245 
especially active or constant participant in 
cell-metabolism, with some such special réle as 
this, rather than as primarily a reservoir of 
hereditary determinants. ° 
The consideration of organic evolution leads 
inevitably to a consideration of the physico- 
chemical nature of living matter and to spec- 
ulations regarding its possible mode of origin 
from non-living matter. In Part I. the author 
discusses briefly some of the supposed steps in 
this evolution. He points out that the process 
must have been prolonged and complex. A 
prerequisite for the appearance of life was the 
production of the vital energy-yielding com- 
pounds, probably by photosynthesis, as well as 
of other compounds of colloidal character 
forming the structural substratum required for 
the metabolic reactions of protoplasm. To 
produce a regulated self-maintaining system of 
this kind, capable of indefinite growth, prob- 
ably required ages of evolution. The role of 
electrolytes in living matter, and the necessity 
for special chemical compounds (catalysers, 
hormones) to control and coordinate the chem- 
ical processes of the primitive protoplasm, are 
among the matters especially discussed in this 
section. Interesting geological evidence is 
presented indicating the existence of an abun- 
dant unicellular flora and fauna (e. g., calear- 
eous bacteria) at extremely remote periods. 
This part of the book is highly suggestive, but 
less complete and authoritative than Part II. 
Many striking observations and generaliza- 
tions are scattered throughout the whole book 
and a masterly survey is given of the paleon- 
tological succession of animal forms. The 
illustrations are especially interesting, partic- 
ularly the reproductions of Knight’s land- 
scapes, at once imaginative and scientifically 
exact, showing the prehistoric monsters in 
their native surroundings. 
Raupu S. Linum 
CLARE UNIVERSITY 
SPECIAL ARTICLES 
NOTE ON A SIMPLE DEVICE FOR ILLUSTRA- 
TING MOLECULAR MOTION 
In experimenting with mercury heated in an 
evacuated glass vessel, I observed that fine 
