NoveMBER 22, 1918] 
significant correlations between these phe- 
nomena and the metabolic gradients which 
are now known to exist in organisms; and to 
propose an explanation of the former in terms 
of these gradients. The metabolic gradients 
were first demonstrated by Child in Planaria; 
subsequently he and his students extended the 
observations to include a large number of adult 
organisms, cells and embryos. This work has 
shown that the anterior, oral or apical end of 
organisms has the highest metabolic rate and 
that this rate decreases along the sagittal axis. 
A gradient in rate of metabolism therefore 
exists along this axis; and to a less extent 
along other axis of symmetry also. This 
fundamental discovery has furnished a basis 
for the interpretation of many hitherto en- 
tirely inexplicable biological facts,2 and I be- 
lieve that it also throws light upon the nature 
of the bioelectric currents. 
The term metabolism is too well under- 
stood to require definition; it commonly signi- 
fies the sum of chemical processes which re- 
sults in the production of new protoplasm or 
other organic compounds, or of energy. 
“Metabolic rate” simply means the rate at 
which these processes take place; and modern 
chemistry, particularly through the study of 
organic and other catalyzers, has taught us 
the supreme importance of rate in any chem- 
ical system. The metabolic rate is generally 
measured either by the rate at which the raw 
materials, particularly oxygen, for the re- 
actions are used up; or by the rate of produc- 
tion of end-products, especially carbon dioxide. 
The extent to which a given mass of proto- 
plasm is actually alive is determined by its 
metabolic rate; these chemical reactions, al- 
ways building and destroying, are the very 
essence of the living; when they sink to a 
rate so low that only the most delicate means 
serve to detect them, the organism is prac- 
tically lifeless, but when they burn intensely, 
1 Child, ‘‘Individuality in Organisms,’’ Univ. of 
Chicago Press, 1915. 
2 Child, Jr. of Morph., XXVIII, p. 65; XXX., 
p. 1; Roux’s Archiv, XXXVII., p. 136; Newman, 
Biol. Bull., XXXII., p. 314, are a few examples 
where such interpretation has been applied. 
SCIENCE 
519 
the most marvelous manifestations of pro- 
toplasm, such as thought, leap forth.® 
The following suggestions are by no means 
entirely new; similar ones have already been 
made by Waller, Child and Tashiro.* In 
collaboration with Mr. A. W. Bellamy of this 
laboratory, I am collecting further data upon 
these matters, and the complete results, to- 
gether with a more extended discussion of the 
literature, will appear later; but a sufficient 
number of facts are already known to justify 
a preliminary statement of the relation be- 
tween metabolic conditions and differences of 
potential found in organisms. 
1. Permanent Differences in Potential—In 
a number of cases we know both the metab- 
olic gradient and the permanent differences 
of electrical potential along the antero-poster- 
ior axis. Thus Mathews® in 1903 discovered 
that the head of hydroids is electro-negative 
to the stem, and that anterior levels are elec- 
tronegative to posterior ones. Later, Child® 
demonstrated that in these animals the head 
or any anterior level has a higher metabolic 
rate than any posterior level.? Hyde® found 
8 Alexander and Cserna, Biochem. Zeitsch., LIII., 
p. 106, have demonstrated that the oxygen con- 
sumption of the brain greatly exceeds that of any 
other part of the body. 
4 Child, ‘‘Individuality in Organisms,’’ p. 63; 
Tashiro, ‘‘ A Chemical Sign of Life,’’ Univ. of Chi- 
eago Press, 1917; Waller, ‘‘Signs of Life from 
their Electrical Aspect,’’? London, 1903. 
5 Am. Jr. of Physiol., VIII., p. 294. 
6 ScleNcE, XXXIX., No. 993. 
7An additional statement regarding the meta- 
bolic gradient in hydroids would seem to be re- 
quired owing to the recent paper of Garcia-Banus 
(Jr. Exp. Zool., XXVI., p. 265), who states that 
apical pieces of the stem of Tubularia do not re- 
generate oral hydranths faster than basal pieces. 
In the summer of 1914 at Woods Hole, while I 
was a student in Professor R. S. Lillie’s class in 
physiology, I performed this experiment with the 
common tubularian hydroid found there, called at 
that time Parypha. I found the hydranths aris- 
ing earlier on the apical pieces; the result was 
clear-cut and definite. The experiment has since 
been repeated at Woods Hole to my personal 
knowledge with the same result as mine. Driesch 
also (Roux’s Archiv, IX., p. 130) found that oral 
