12 
PHYSIOLOGY: FORBES AND RAPPLEYE 
has come to the conclusion that Griineisen's theory can not be more 
than a first approximation. This conclusion will not be altered by 
using the values of the table above instead of those of Beckman. 
The theory of Griineisen is incomplete in the sense that it gives the 
pressure coefficient of resistance in terms of the temperature coefficient 
as well as several thermodynamic constants. I hope to show at some 
length elsewhere that both the temperature and the pressure coeffi- 
cient of resistance may be calculated with better agreement than by 
Griineisen's formula by putting the proportional change of resistance 
in any direction equal to twice the proportional change of average am- 
plitude of atomic vibration. This is capable of theoretical explanation 
on the ground that when the atoms are at rest the electrons pass freely 
from atom to atom, but when the separation of the atoms by haphazard 
heat agitation becomes too great, the electrons encounter difficulty 
in jumping from atom to atom. 
The expenses of this investigation were in large part met by generous 
appropriations from the Bache Fund of the National Academy of Sci- 
ences, and from the Rumford Fund of the American Academy of Arts 
and Sciences. 
' Lisell, E., Inaug. Dis,, Upsala, 1902; and Beckman, B., Inaug. Dis., Upsala, 1911; Ark. 
Mat. Astr. Fys., 7, 1912, No. 42 (1-18); Ann. Physik., Leipzig, 46, 1915, (481-502) and 
(931-941); Physik. Zs., Leipzig, 16, 1915, (59-63). 
2 Griineisen, E., Berlin, Verh. D. physik. Ges., 15, 1913, (186-200). 
THE RATE OF DISCHARGE OF CENTRAL NEURONES 
By Alexander Forbes and W. C. Rappleye 
LABORATORY OF PHYSIOLOGY. HARVARD MEDICAL SCHOOL 
Communicated by W. B. Cannon, November 27, 1916 
The frequency of nerve impulses discharged from the central nerv- 
ous system in voluntary and reflex contraction of the skeletal mus- 
cles presents a problem concerning which great difference of opinion 
is found among investigators. Piper, studying the electrical disturb- 
ance with a string galvanometer, has shown that in human muscles a 
fairly regular series of action currents with a rhythm of about 50 per 
second accompanies voluntary contraction. He inferred from this 
that the central nervous system sends to the muscle 50 impulses per 
second. 
Buchanan, chiefly on the basis of experiments on frogs, reached the 
conclusion that the observed rhythm is not that of the motor nerve 
impulses but is dependent on the condition of the muscle itself. 
