PHYSIOLOGY: E. B. HARVEY 
15 
quency of nerve impulses discharged from the ganghon cells in volun- 
tary contraction must lie between 300 and 5000 per second. 
The complete paper will appear in the American Journal of Physiology, 
January, 1917. 
A PHYSIOLOGICAL STUDY OF NOCTILUCA, WITH SPECIAL REFER- 
ENCE TO LIGHT PRODUCTION, ANAESTHESIA 
AND SPECIFIC GRAVITY 
By Ethel Browne Harvey 
CORNELL UNIVERSITY MEDICAL SCHOOL. NEW YORK CITY. AND DEPARTMENT OF 
MARINE BIOLOGY. CARNEGIE INSTITUTION OF WASHINGTON 
Communicated by A. G. Mayer. December 5. 1916 
The specific gravity of Noctiluca is less than that of sea water, so 
that normally the animals float at the surface. They contain no air 
bubbles or large oil drops, and their lower specific gravity must there- 
fore be due to a lower salt content than the sea water. In more con- 
centrated sea water, the animals shrink and in more dilute sea water 
they swell; the plasma membrane therefore has the usual semipermea- 
bility toward the balanced salts of sea water, i.e., permeability to water 
and impermeabihty to salts. When placed in a mixture of 4 sea water; 
6 fresh water, the animals sink, their salt content being now greater 
than that of the surrounding medium, but later they rise to the sur- 
face, a process independent of the movement of the tentacle. They 
must therefore have absorbed water not only until their salt content 
is the same as that of the surrounding medium (when they should still 
sink), but enough water to make their salt content again less than the 
4 S.W.: 6 f.w. mixture, thus re-establishing their normal relation to the 
surrounding medium. This water must be absorbed against the os- 
motic pressure of the salts of sea water, a process contrary to physical 
laws. The animals can not only lessen their specific gravity, but they 
can also increase it, as is shown by the fact that on windy days they 
sink far beneath the surface of the sea. Anesthetics, acids and alka- 
lies, KCN, and the pure solutions of the salts of sea water do not inter- 
fere with this regulatory mechanism except when they cause irrever- 
sible changes and death of the cells; dead Noctiluca always sinks to the 
bottom. 
Light production in Noctiluca normally occurs only on stimulation 
of any kind, and is a momentary bright flash; dying animals produce a 
bright steady glow. The luminescence is traceable to points of light 
coming from granules in the protoplasm. No substances were found 
which would cause a rhythmic flashing, comparable to the rhythmic 
